Optimizer Hints | TiDB 文档中心

相关文章推荐

憨厚的硬盘 · Optimizer Hints | ...· 22 小时前 ·

精明的饺子 · java.io.FileNotFoundEx ...· 8 月前 ·

另类的牙膏 · Perl 错误处理 | 菜鸟教程· 1 年前 ·

八块腹肌的排球 · PHP ...· 1 年前 ·

玩滑板的牛肉面 · VBA学习笔记3:循环语句 - 知乎· 1 年前 ·

</noscript><noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-TPX49SBK" height="0" width="0" style="display: none; visibility: hidden" aria-hidden="true"/></noscript><div id="___gatsby"><div style="outline:none" tabindex="-1" id="gatsby-focus-wrapper"><header class="MuiPaper-root MuiPaper-elevation MuiPaper-elevation4 MuiAppBar-root MuiAppBar-colorPrimary MuiAppBar-positionFixed doc-site-header mui-fixed css-1xx3vsu"><div class="MuiToolbar-root MuiToolbar-gutters MuiToolbar-regular css-j6gnra"><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeMedium css-iuftj9" tabindex="0" type="button" aria-label="menu"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-vubbuv" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="MenuIcon"><path d="M3 18h18v-2H3v2zm0-5h18v-2H3v2zm0-7v2h18V6H3z"/></svg></button><div class="MuiBox-root css-13tqxrv"><a style="text-decoration:none" href="/zh/"><svg width="152" height="36" viewbox="0 0 152 36" fill="none"><g clip-path="url(#clip0_789_1365)"><path d="M0 26.9605V9.04959C0 9.01208 0.0187549 8.98395 0.0468872 8.96519L15.5478 0.00973267C15.5759 -0.00902222 15.6134 -0.00902222 15.6416 0.00973267L31.1425 8.95581C31.1706 8.97457 31.1894 9.0027 31.1894 9.04021V26.9511C31.1894 26.9886 31.1706 27.0168 31.1425 27.0355L15.6416 35.991C15.6134 36.0097 15.5759 36.0097 15.5478 35.991L0.0468872 27.0355C0.0187549 27.0168 0 26.9886 0 26.9605Z" fill="#DC150B"/><path d="M10.3808 15.0336C10.3714 15.0242 10.3527 15.0149 10.3433 15.0242L5.25136 17.9688H5.2326C5.21384 17.9688 5.20447 17.9594 5.20447 17.9406V12.0047C5.20447 11.9953 5.21384 11.986 5.22322 11.9766L5.22322 11.9766L15.5572 6.01253C15.5665 6.00315 15.5759 6.00315 15.5853 6.01253L20.7241 8.9758L20.7335 8.98518C20.7429 8.99455 20.7335 9.01331 20.7241 9.02268L15.5759 11.9953C15.5665 12.0047 15.5572 12.0141 15.5572 12.0235V29.9625V29.9813C15.5478 29.9906 15.529 30 15.5197 29.9906L10.3902 27.0368C10.3902 27.0274 10.3808 27.018 10.3808 27.0086V15.0524V15.0336Z" fill="white"/><path d="M20.7992 26.9992C20.7804 26.9992 20.7616 26.9805 20.7616 26.9617V15.0336C20.7616 15.0149 20.771 15.0055 20.7804 14.9961L25.9286 12.0235L25.9286 12.0235C25.938 12.0141 25.938 12.0141 25.9474 12.0141C25.9661 12.0141 25.9849 12.0328 25.9849 12.0516V23.9797C25.9849 23.9985 25.9755 24.0078 25.9661 24.0172L20.8179 26.9899C20.8085 26.9992 20.8085 26.9992 20.7992 26.9992Z" fill="white"/></g><path d="M37.1894 12.4971H42.0242V26.9998H45.4248V12.4971H50.2596V9.37683H37.1894V12.4971Z" fill="black"/><path d="M53.6372 9C53.1197 9 52.6672 9.18709 52.2887 9.55826C51.9102 9.92943 51.7151 10.3941 51.7151 10.9373C51.7151 11.4503 51.9073 11.8999 52.2858 12.2802C52.6643 12.6574 53.1167 12.8505 53.6342 12.8505C54.1517 12.8505 54.5775 12.6574 54.9501 12.2802C55.3227 11.903 55.509 11.4503 55.509 10.9373C55.509 10.3941 55.3257 9.93245 54.9619 9.56128C54.5982 9.19011 54.1517 9.00302 53.6372 9.00302V9Z" fill="black"/><path d="M55.2895 14.3592H51.9864V27H55.2895V14.3592Z" fill="black"/><path d="M64.3322 9.37683H58.2613V26.9998H64.3322C66.9492 26.9998 69.028 26.2031 70.5124 24.6309C71.9939 23.0587 72.748 20.8921 72.748 18.1883C72.748 15.4845 71.9969 13.2967 70.5124 11.7336C69.028 10.1705 66.9492 9.37683 64.3322 9.37683ZM61.6619 12.4971H64.2109C65.9024 12.4971 67.1798 12.998 68.0137 13.9847C68.8506 14.9775 69.2734 16.3566 69.2734 18.0857C69.2734 19.8148 68.8476 21.2512 68.0108 22.3013C67.1769 23.3454 65.8994 23.8765 64.208 23.8765H61.659V12.494L61.6619 12.4971Z" fill="black"/><path d="M86.5964 19.1388C86.0346 18.4418 85.3663 17.9409 84.6152 17.6512V17.621C86.1883 16.8424 86.9838 15.566 86.9838 13.8278C86.9838 12.479 86.5461 11.3866 85.6856 10.5839C84.8251 9.78421 83.5566 9.37683 81.9154 9.37683H74.7948V26.9998H81.8681C83.6068 26.9998 84.9907 26.5652 85.9784 25.7082C86.972 24.8482 87.4747 23.6261 87.4747 22.075C87.4747 20.8468 87.179 19.8601 86.5994 19.1388H86.5964ZM78.1185 16.5256V12.1953H81.4718C82.1105 12.1953 82.628 12.3884 83.0095 12.7686C83.388 13.1489 83.5802 13.68 83.5802 14.3499C83.5802 15.0198 83.3909 15.5569 83.0184 15.9432C82.6458 16.3294 82.1105 16.5256 81.4216 16.5256H78.1156H78.1185ZM83.9972 21.8245C83.9972 22.5276 83.7872 23.101 83.3762 23.5295C82.9651 23.958 82.356 24.1753 81.5724 24.1753H78.1215V19.3471H81.5724C82.3235 19.3471 82.9237 19.5794 83.3525 20.0411C83.7813 20.5028 84.0001 21.1033 84.0001 21.8215L83.9972 21.8245Z" fill="black"/><path d="M97.3306 26.5V9.7H102.299C107.771 9.7 111.083 12.868 111.083 18.1C111.083 23.332 107.771 26.5 102.299 26.5H97.3306ZM102.299 24.364C106.331 24.364 108.659 22.06 108.659 18.1C108.659 14.14 106.331 11.836 102.299 11.836H99.7066V24.364H102.299ZM118.968 26.764C115.464 26.764 112.824 24.052 112.824 20.5C112.824 16.948 115.464 14.236 118.968 14.236C122.472 14.236 125.112 16.948 125.112 20.5C125.112 24.052 122.472 26.764 118.968 26.764ZM118.968 24.628C121.152 24.628 122.736 22.876 122.736 20.5C122.736 18.124 121.152 16.372 118.968 16.372C116.784 16.372 115.2 18.124 115.2 20.5C115.2 22.876 116.784 24.628 118.968 24.628ZM132.772 26.764C129.22 26.764 126.7 24.124 126.7 20.5C126.7 16.876 129.22 14.236 132.772 14.236C135.652 14.236 137.884 15.964 138.244 18.532H135.844C135.532 17.236 134.332 16.372 132.772 16.372C130.588 16.372 129.076 18.076 129.076 20.5C129.076 22.9 130.588 24.628 132.772 24.628C134.332 24.628 135.532 23.764 135.844 22.468H138.244C137.884 25.036 135.652 26.764 132.772 26.764ZM144.557 26.764C141.677 26.764 139.781 25.108 139.709 22.732H142.085C142.229 23.956 142.973 24.724 144.581 24.724C145.733 24.724 146.765 24.34 146.765 23.332C146.765 22.588 146.333 22.06 145.157 21.7L143.333 21.172C141.173 20.548 140.093 19.3 140.093 17.716C140.093 15.604 141.965 14.236 144.413 14.236C146.885 14.236 148.685 15.7 148.829 17.74H146.453C146.285 16.828 145.445 16.204 144.341 16.204C143.261 16.204 142.469 16.804 142.469 17.716C142.469 18.412 142.925 18.868 144.245 19.228L146.069 19.732C148.109 20.308 149.141 21.556 149.141 23.188C149.141 25.396 147.197 26.764 144.557 26.764Z" fill="black"/><defs><clippath id="clip0_789_1365"><rect width="31.1894" height="36" fill="white"/></clippath></defs></svg></a></div><div class="css-2iqpys"><div class="MuiBox-root css-irbys9"><a style="text-decoration:none" hreflang="zh" href="/zh/tidb/stable/"><div class="MuiTypography-root MuiTypography-body1 css-195ggqq">TiDB</div></a></div><div class="MuiBox-root css-kiou0g"><a class="MuiTypography-root MuiTypography-body1 css-ae3kd9" target="_blank" href="https://asktug.com/" style="text-decoration:none"><div class="MuiTypography-root MuiTypography-body1 css-195ggqq">社区</div></a></div><div class="MuiBox-root css-kiou0g"><a class="MuiTypography-root MuiTypography-body1 css-ae3kd9" target="_blank" href="https://cn.pingcap.com/contact/" style="text-decoration:none"><div class="MuiTypography-root MuiTypography-body1 css-195ggqq">联系我们</div></a></div><div class="MuiBox-root css-kiou0g"><a class="MuiTypography-root MuiTypography-body1 css-ae3kd9" target="_blank" href="https://cn.pingcap.com/product/#SelectProduct" style="text-decoration:none"><div class="MuiTypography-root MuiTypography-body1 css-195ggqq"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="DownloadIcon"><path d="M5 20h14v-2H5v2zM19 9h-4V3H9v6H5l7 7 7-7z"/></svg></div></a></div></div><div class="MuiBox-root css-1vn3uc0"><button class="MuiButtonBase-root MuiButton-root MuiButton-text MuiButton-textInherit MuiButton-sizeMedium MuiButton-textSizeMedium MuiButton-colorInherit MuiButton-disableElevation css-tjg32r" tabindex="0" type="button" id="header-nav-items" aria-haspopup="true"><span class="MuiButton-startIcon MuiButton-iconSizeMedium css-1l6c7y9"><svg width="152" height="36" viewbox="0 0 152 36" fill="none"><g clip-path="url(#clip0_789_1365)"><path d="M0 26.9605V9.04959C0 9.01208 0.0187549 8.98395 0.0468872 8.96519L15.5478 0.00973267C15.5759 -0.00902222 15.6134 -0.00902222 15.6416 0.00973267L31.1425 8.95581C31.1706 8.97457 31.1894 9.0027 31.1894 9.04021V26.9511C31.1894 26.9886 31.1706 27.0168 31.1425 27.0355L15.6416 35.991C15.6134 36.0097 15.5759 36.0097 15.5478 35.991L0.0468872 27.0355C0.0187549 27.0168 0 26.9886 0 26.9605Z" fill="#DC150B"/><path d="M10.3808 15.0336C10.3714 15.0242 10.3527 15.0149 10.3433 15.0242L5.25136 17.9688H5.2326C5.21384 17.9688 5.20447 17.9594 5.20447 17.9406V12.0047C5.20447 11.9953 5.21384 11.986 5.22322 11.9766L5.22322 11.9766L15.5572 6.01253C15.5665 6.00315 15.5759 6.00315 15.5853 6.01253L20.7241 8.9758L20.7335 8.98518C20.7429 8.99455 20.7335 9.01331 20.7241 9.02268L15.5759 11.9953C15.5665 12.0047 15.5572 12.0141 15.5572 12.0235V29.9625V29.9813C15.5478 29.9906 15.529 30 15.5197 29.9906L10.3902 27.0368C10.3902 27.0274 10.3808 27.018 10.3808 27.0086V15.0524V15.0336Z" fill="white"/><path d="M20.7992 26.9992C20.7804 26.9992 20.7616 26.9805 20.7616 26.9617V15.0336C20.7616 15.0149 20.771 15.0055 20.7804 14.9961L25.9286 12.0235L25.9286 12.0235C25.938 12.0141 25.938 12.0141 25.9474 12.0141C25.9661 12.0141 25.9849 12.0328 25.9849 12.0516V23.9797C25.9849 23.9985 25.9755 24.0078 25.9661 24.0172L20.8179 26.9899C20.8085 26.9992 20.8085 26.9992 20.7992 26.9992Z" fill="white"/></g><path d="M37.1894 12.4971H42.0242V26.9998H45.4248V12.4971H50.2596V9.37683H37.1894V12.4971Z" fill="black"/><path d="M53.6372 9C53.1197 9 52.6672 9.18709 52.2887 9.55826C51.9102 9.92943 51.7151 10.3941 51.7151 10.9373C51.7151 11.4503 51.9073 11.8999 52.2858 12.2802C52.6643 12.6574 53.1167 12.8505 53.6342 12.8505C54.1517 12.8505 54.5775 12.6574 54.9501 12.2802C55.3227 11.903 55.509 11.4503 55.509 10.9373C55.509 10.3941 55.3257 9.93245 54.9619 9.56128C54.5982 9.19011 54.1517 9.00302 53.6372 9.00302V9Z" fill="black"/><path d="M55.2895 14.3592H51.9864V27H55.2895V14.3592Z" fill="black"/><path d="M64.3322 9.37683H58.2613V26.9998H64.3322C66.9492 26.9998 69.028 26.2031 70.5124 24.6309C71.9939 23.0587 72.748 20.8921 72.748 18.1883C72.748 15.4845 71.9969 13.2967 70.5124 11.7336C69.028 10.1705 66.9492 9.37683 64.3322 9.37683ZM61.6619 12.4971H64.2109C65.9024 12.4971 67.1798 12.998 68.0137 13.9847C68.8506 14.9775 69.2734 16.3566 69.2734 18.0857C69.2734 19.8148 68.8476 21.2512 68.0108 22.3013C67.1769 23.3454 65.8994 23.8765 64.208 23.8765H61.659V12.494L61.6619 12.4971Z" fill="black"/><path d="M86.5964 19.1388C86.0346 18.4418 85.3663 17.9409 84.6152 17.6512V17.621C86.1883 16.8424 86.9838 15.566 86.9838 13.8278C86.9838 12.479 86.5461 11.3866 85.6856 10.5839C84.8251 9.78421 83.5566 9.37683 81.9154 9.37683H74.7948V26.9998H81.8681C83.6068 26.9998 84.9907 26.5652 85.9784 25.7082C86.972 24.8482 87.4747 23.6261 87.4747 22.075C87.4747 20.8468 87.179 19.8601 86.5994 19.1388H86.5964ZM78.1185 16.5256V12.1953H81.4718C82.1105 12.1953 82.628 12.3884 83.0095 12.7686C83.388 13.1489 83.5802 13.68 83.5802 14.3499C83.5802 15.0198 83.3909 15.5569 83.0184 15.9432C82.6458 16.3294 82.1105 16.5256 81.4216 16.5256H78.1156H78.1185ZM83.9972 21.8245C83.9972 22.5276 83.7872 23.101 83.3762 23.5295C82.9651 23.958 82.356 24.1753 81.5724 24.1753H78.1215V19.3471H81.5724C82.3235 19.3471 82.9237 19.5794 83.3525 20.0411C83.7813 20.5028 84.0001 21.1033 84.0001 21.8215L83.9972 21.8245Z" fill="black"/><path d="M97.3306 26.5V9.7H102.299C107.771 9.7 111.083 12.868 111.083 18.1C111.083 23.332 107.771 26.5 102.299 26.5H97.3306ZM102.299 24.364C106.331 24.364 108.659 22.06 108.659 18.1C108.659 14.14 106.331 11.836 102.299 11.836H99.7066V24.364H102.299ZM118.968 26.764C115.464 26.764 112.824 24.052 112.824 20.5C112.824 16.948 115.464 14.236 118.968 14.236C122.472 14.236 125.112 16.948 125.112 20.5C125.112 24.052 122.472 26.764 118.968 26.764ZM118.968 24.628C121.152 24.628 122.736 22.876 122.736 20.5C122.736 18.124 121.152 16.372 118.968 16.372C116.784 16.372 115.2 18.124 115.2 20.5C115.2 22.876 116.784 24.628 118.968 24.628ZM132.772 26.764C129.22 26.764 126.7 24.124 126.7 20.5C126.7 16.876 129.22 14.236 132.772 14.236C135.652 14.236 137.884 15.964 138.244 18.532H135.844C135.532 17.236 134.332 16.372 132.772 16.372C130.588 16.372 129.076 18.076 129.076 20.5C129.076 22.9 130.588 24.628 132.772 24.628C134.332 24.628 135.532 23.764 135.844 22.468H138.244C137.884 25.036 135.652 26.764 132.772 26.764ZM144.557 26.764C141.677 26.764 139.781 25.108 139.709 22.732H142.085C142.229 23.956 142.973 24.724 144.581 24.724C145.733 24.724 146.765 24.34 146.765 23.332C146.765 22.588 146.333 22.06 145.157 21.7L143.333 21.172C141.173 20.548 140.093 19.3 140.093 17.716C140.093 15.604 141.965 14.236 144.413 14.236C146.885 14.236 148.685 15.7 148.829 17.74H146.453C146.285 16.828 145.445 16.204 144.341 16.204C143.261 16.204 142.469 16.804 142.469 17.716C142.469 18.412 142.925 18.868 144.245 19.228L146.069 19.732C148.109 20.308 149.141 21.556 149.141 23.188C149.141 25.396 147.197 26.764 144.557 26.764Z" fill="black"/><defs><clippath id="clip0_789_1365"><rect width="31.1894" height="36" fill="white"/></clippath></defs></svg></span><span class="MuiButton-endIcon MuiButton-iconSizeMedium css-pt151d"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-vubbuv" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="KeyboardArrowDownIcon"><path d="M7.41 8.59 12 13.17l4.59-4.58L18 10l-6 6-6-6 1.41-1.41z"/></svg></span></button></div><div class="css-1w2hxsf"><div class="MuiBox-root css-19itmc6"><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeMedium css-jwr93t" tabindex="0" type="button"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-vubbuv" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="TranslateIcon"><path d="m12.87 15.07-2.54-2.51.03-.03c1.74-1.94 2.98-4.17 3.71-6.53H17V4h-7V2H8v2H1v1.99h11.17C11.5 7.92 10.44 9.75 9 11.35 8.07 10.32 7.3 9.19 6.69 8h-2c.73 1.63 1.73 3.17 2.98 4.56l-5.09 5.02L4 19l5-5 3.11 3.11.76-2.04zM18.5 10h-2L12 22h2l1.12-3h4.75L21 22h2l-4.5-12zm-2.62 7 1.62-4.33L19.12 17h-3.24z"/></svg></button><button class="MuiButtonBase-root MuiButton-root MuiButton-text MuiButton-textInherit MuiButton-sizeMedium MuiButton-textSizeMedium MuiButton-colorInherit MuiButton-disableElevation css-1r5wmim" tabindex="0" type="button" id="header-lang-switch" aria-haspopup="true"><span class="MuiButton-startIcon MuiButton-iconSizeMedium css-1l6c7y9"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-1msahp5" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="TranslateIcon"><path d="m12.87 15.07-2.54-2.51.03-.03c1.74-1.94 2.98-4.17 3.71-6.53H17V4h-7V2H8v2H1v1.99h11.17C11.5 7.92 10.44 9.75 9 11.35 8.07 10.32 7.3 9.19 6.69 8h-2c.73 1.63 1.73 3.17 2.98 4.56l-5.09 5.02L4 19l5-5 3.11 3.11.76-2.04zM18.5 10h-2L12 22h2l1.12-3h4.75L21 22h2l-4.5-12zm-2.62 7 1.62-4.33L19.12 17h-3.24z"/></svg></span><span class="MuiButton-endIcon MuiButton-iconSizeMedium css-pt151d"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-1msahp5" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="KeyboardArrowDownIcon"><path d="M7.41 8.59 12 13.17l4.59-4.58L18 10l-6 6-6-6 1.41-1.41z"/></svg></span></button></div><div class="css-1iegyem"><div class="MuiBox-root css-0"><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeMedium css-iuftj9" tabindex="0" type="button"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-vubbuv" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="SearchIcon"><path d="M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"/></svg></button><form class="MuiBox-root css-1dl8tgy" novalidate="" autocomplete="off"><div class="MuiFormControl-root MuiFormControl-fullWidth MuiTextField-root css-7omol5"><div class="MuiInputBase-root MuiOutlinedInput-root MuiInputBase-colorPrimary MuiInputBase-fullWidth MuiInputBase-formControl MuiInputBase-sizeSmall MuiInputBase-adornedStart css-784vi5"><div class="MuiInputAdornment-root MuiInputAdornment-positionStart MuiInputAdornment-outlined MuiInputAdornment-sizeSmall css-1a6giau"><span class="notranslate"></span><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeSmall css-1k33q06" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="SearchIcon"><path d="M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"/></svg></div><input type="search" aria-invalid="false" id="doc-search" placeholder="搜索文档" value="" class="MuiInputBase-input MuiOutlinedInput-input MuiInputBase-inputTypeSearch MuiInputBase-inputSizeSmall MuiInputBase-inputAdornedStart css-kx70l9"/><fieldset aria-hidden="true" class="MuiOutlinedInput-notchedOutline css-igs3ac"><legend class="css-hdw1oc"><span class="notranslate"></span></legend></fieldset></div></div></form></div></div></div></div><div class="MuiBox-root css-pk5svg"><a href="https://labs.pingcap.com/?utm_source=docs&amp;utm_medium=direct&amp;utm_campaign=labs_zh_lp_04" target="_blank" class="css-1oh5qm"><div class="css-vb6e92"><div class="MuiBox-root css-0">🚀</div><span class="MuiTypography-root MuiTypography-body2 css-1xpq684">探索全新的 TiDB Labs，直接在浏览器中学习分布式 SQL 数据库并构建 RAG 应用。</span></div></a></div></header><div class="PingCAP-Doc doc-feature-banner MuiBox-root css-88zx00"><div class="MuiBox-root css-hboir5"><aside class="MuiBox-root css-2tzg8"><div class="MuiBox-root css-xskeex"><button class="MuiButtonBase-root MuiButton-root MuiButton-text MuiButton-textPrimary MuiButton-sizeMedium MuiButton-textSizeMedium MuiButton-disableElevation css-1q0sqyi" tabindex="0" type="button" id="version-select-button" aria-haspopup="true"><div class="MuiTypography-root MuiTypography-body1 css-1alj0g7">v8.5</div><span class="MuiButton-endIcon MuiButton-iconSizeMedium css-pt151d"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium css-1rrdqpg" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></span></button><ul role="tree" id="left-nav-treeview" aria-multiselectable="false" class="MuiTreeView-root css-12mehxg" tabindex="0" aria-label="left navigation"><a class="MuiTypography-root MuiTypography-body1 css-ae3kd9" target="_blank" href="https://docs.pingcap.com/zh" style="text-decoration:none;width:100%;color:inherit"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">文档中心</div></div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">关于 TiDB</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">快速上手</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">应用开发</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-4" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">部署标准集群</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-5" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">数据迁移</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-6" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">数据同步</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-7" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">运维操作</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-8" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">监控与告警</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-9" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">故障诊断</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-10" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">性能调优</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-10-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">优化手册</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-10-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">配置调优</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-10-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 性能调优</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/sql-tuning-overview/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-10-2-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 性能调优概览</div></div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-10-2-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">理解 TiDB 执行计划</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-10-2-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 优化流程</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-10-2-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">控制执行计划</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/control-execution-plan/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-10-2-3-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">控制执行计划概览</div></div></div></div></div></div></li></a><a aria-current="page" style="text-decoration:none;width:100%;color:inherit" class="" href="/zh/tidb/stable/optimizer-hints/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-selected="true" id="left-nav-treeview-0-0-10-2-3-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded Mui-selected" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">Optimizer Hints</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/sql-plan-management/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-10-2-3-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">执行计划管理</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/blocklist-control-plan/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-10-2-3-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">优化规则及表达式下推的黑名单</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/optimizer-fix-controls/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-10-2-3-4" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">Optimizer Fix Controls</div></div></div></div></div></div></li></a></div></div></ul></li></div></div></ul></li></div></div></ul></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-11" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">教程</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-12" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">TiDB 工具</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">参考指南</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-14" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">常见问题解答 (FAQ)</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-15" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">版本发布历史</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/glossary/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-16" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">术语表</div></div></div></div></div></div></li></a></ul></div></aside><main class="MuiBox-root css-sb2sd0"><div class="MuiBox-root css-w0vdto"><div class="css-1q5cbag"><div class="MuiBox-root css-was4pq"><div class="MuiContainer-root MuiContainer-maxWidthLg MuiContainer-disableGutters doc-content css-5csqms"><div class="markdown-body MuiBox-root css-0"><h1 id="optimizer-hints" style="position:relative">Optimizer Hints<a href="#optimizer-hints" aria-label="optimizer hints permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h1><p>TiDB 支持 Optimizer Hints 语法，它基于 MySQL 5.7 中介绍的类似 comment 的语法，例如 <code>/*+ HINT_NAME(t1, t2) */</code>。当 TiDB 优化器选择的不是最优查询计划时，建议使用 Optimizer Hints。</p><p>如果遇到 Hint 无法生效的情况，请参考<a href="#%E5%B8%B8%E8%A7%81-hint-%E4%B8%8D%E7%94%9F%E6%95%88%E9%97%AE%E9%A2%98%E6%8E%92%E6%9F%A5">常见 Hint 不生效问题排查</a>。</p><h2 id="语法" style="position:relative">语法<a href="#%E8%AF%AD%E6%B3%95" aria-label="语法 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h2><p>Optimizer Hints 不区分大小写，通过 <code>/*+ ... */</code> 注释的形式跟在 <code>SELECT</code>、<code>INSERT</code>、<code>UPDATE</code> 或 <code>DELETE</code> 关键字的后面。</p><p>多个不同的 Hint 之间需用逗号隔开，例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t1, idx1), HASH_AGG(), HASH_JOIN(t1) */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.b; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>可以通过 <a href="/zh/tidb/stable/sql-statement-explain/"><code>Explain</code></a>/<a href="/zh/tidb/stable/sql-statement-explain-analyze/"><code>Explain Analyze</code></a> 语句的输出，来查看 Optimizer Hints 对查询执行计划的影响。</p><p>如果 Optimizer Hints 包含语法错误或不完整，查询语句不会报错，而是按照没有 Optimizer Hints 的情况执行。如果 Hint 不适用于当前语句，TiDB 会返回 Warning，用户可以在查询结束后通过 <code>Show Warnings</code> 命令查看具体信息。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>如果注释不是跟在指定的关键字后，会被当作是普通的 MySQL comment，注释不会生效，且不会上报 warning。</p></div></div></div><p>TiDB 目前支持的 Optimizer Hints 根据生效范围的不同可以划分为两类：第一类是在查询块范围生效的 Hint，例如 <a href="#hash_agg"><code>/*+ HASH_AGG() */</code></a>；第二类是在整个查询范围生效的 Hint，例如 <a href="#memory_quotan"><code>/*+ MEMORY_QUOTA(1024 MB)*/</code></a>。</p><p>每条语句中每一个查询和子查询都对应着一个不同的查询块，每个查询块有自己对应的名字。以下面这条语句为例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t1, (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>该查询语句有 3 个查询块，最外面一层 <code>SELECT</code> 所在的查询块的名字为 <code>sel_1</code>，两个 <code>SELECT</code> 子查询的名字依次为 <code>sel_2</code> 和 <code>sel_3</code>。其中数字序号根据 <code>SELECT</code> 出现的位置从左到右计数。如果分别用 <code>DELETE</code> 和 <code>UPDATE</code> 查询替代第一个 <code>SELECT</code> 查询，则对应的查询块名字分别为 <code>del_1</code> 和 <code>upd_1</code>。</p><h2 id="查询块范围生效的-hint" style="position:relative">查询块范围生效的 Hint<a href="#%E6%9F%A5%E8%AF%A2%E5%9D%97%E8%8C%83%E5%9B%B4%E7%94%9F%E6%95%88%E7%9A%84-hint" aria-label="查询块范围生效的 hint permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h2><p>这类 Hint 可以跟在查询语句中<strong>任意</strong> <code>SELECT</code>、<code>UPDATE</code> 或 <code>DELETE</code> 关键字的后面。通过在 Hint 中使用查询块名字可以控制 Hint 的生效范围，以及准确标识查询中的每一个表（有可能表的名字或者别名相同），方便明确 Hint 的参数指向。若不显式地在 Hint 中指定查询块，Hint 默认作用于当前查询块。以如下查询为例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN(@sel_1 t1@sel_1, t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> t1.a, t1.b <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.a) t1, t t3 <span class="hljs-keyword">WHERE</span> t1.b <span class="hljs-operator">=</span> t3.b; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>该 Hint 在 <code>sel_1</code> 这个查询块中生效，参数分别为 <code>sel_1</code> 中的 <code>t1</code> 表（<code>sel_2</code> 中也有一个 <code>t1</code> 表）和 <code>t3</code> 表。</p><p>如上例所述，在 Hint 中使用查询块名字的方式有两种：第一种是作为 Hint 的第一个参数，与其他参数用空格隔开。除 <code>QB_NAME</code> 外，本节所列的所有 Hint 除自身明确列出的参数外都有一个隐藏的可选参数 <code>@QB_NAME</code>，通过使用这个参数可以指定该 Hint 的生效范围；第二种在 Hint 中使用查询块名字的方式是在参数中的某一个表名后面加 <code>@QB_NAME</code>，用以明确指出该参数是哪个查询块中的表。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>Hint 声明的位置必须在指定生效的查询块之中或之前，不能是在之后的查询块中，否则无法生效。</p></div></div></div><h3 id="qb_name" style="position:relative">QB_NAME<a href="#qb_name" aria-label="qb_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>当查询语句是包含多层嵌套子查询的复杂语句时，识别某个查询块的序号和名字很可能会出错，Hint <code>QB_NAME</code> 可以方便我们使用查询块。<code>QB_NAME</code> 是 Query Block Name 的缩写，用于为某个查询块指定新的名字，同时查询块原本默认的名字依然有效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(QB1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t1, (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t) t2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>这条 Hint 将最外层 <code>SELECT</code> 查询块的命名为 <code>QB1</code>，此时 <code>QB1</code> 和默认名称 <code>sel_1</code> 对于这个查询块来说都是有效的。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>上述例子中，如果指定的 <code>QB_NAME</code> 为 <code>sel_2</code>，并且不给原本 <code>sel_2</code> 对应的第二个查询块指定新的 <code>QB_NAME</code>，则第二个查询块的默认名字 <code>sel_2</code> 会失效。</p></div></div></div><h3 id="merge_joint1_name--tl_name-" style="position:relative">MERGE_JOIN(t1_name [, tl_name ...])<a href="#merge_joint1_name--tl_name-" aria-label="merge_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>MERGE_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Sort Merge Join 算法。这个算法通常会占用更少的内存，但执行时间会更久。当数据量太大，或系统内存不足时，建议尝试使用。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MERGE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>MERGE_JOIN</code> 的别名是 <code>TIDB_SMJ</code>，在 3.0.x 及之前版本仅支持使用该别名；之后的版本同时支持使用这两种名称，但推荐使用 <code>MERGE_JOIN</code>。</p></div></div></div><h3 id="no_merge_joint1_name--tl_name-" style="position:relative">NO_MERGE_JOIN(t1_name [, tl_name ...])<a href="#no_merge_joint1_name--tl_name-" aria-label="no_merge_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_MERGE_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表不要使用 Sort Merge Join 算法。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_MERGE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="inl_joint1_name--tl_name-" style="position:relative">INL_JOIN(t1_name [, tl_name ...])<a href="#inl_joint1_name--tl_name-" aria-label="inl_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>部分情况下 <code>INL_JOIN</code> Hint 可能无法生效，详情请参阅 <a href="#inl_join-hint-%E4%B8%8D%E7%94%9F%E6%95%88"><code>INL_JOIN</code> Hint 不生效</a>。</p></div></div></div><p><code>INL_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Index Nested Loop Join 算法。这个算法可能会在某些场景更快，消耗更少系统资源，有的场景会更慢，消耗更多系统资源。对于外表经过 WHERE 条件过滤后结果集较小（小于 1 万行）的场景，可以尝试使用。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>在上面的 SQL 中，<code>INL_JOIN(t1, t2)</code> 会提示优化器对 <code>t1</code> 和 <code>t2</code> 使用 Index Nested Loop Join 算法。注意它并不是指 <code>t1</code> 和 <code>t2</code> 之间使用 Index Nested Loop Join 算法，而是 <code>t1</code> 和 <code>t2</code> 分别与其他表 (<code>t3</code>) 之间使用 Index Nested Loop Join 算法。</p><p><code>INL_JOIN()</code> 中的参数是建立查询计划时内表的候选表，比如 <code>INL_JOIN(t1)</code> 只会考虑使用 <code>t1</code> 作为内表构建查询计划。表如果指定了别名，就只能使用表的别名作为 <code>INL_JOIN()</code> 的参数；如果没有指定别名，则用表的本名作为其参数。比如在 <code>SELECT /*+ INL_JOIN(t1) */ * FROM t t1, t t2 WHERE t1.a = t2.b;</code> 中，<code>INL_JOIN()</code> 的参数只能使用 <code>t</code> 的别名 <code>t1</code> 或 <code>t2</code>，不能用 <code>t</code>。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>INL_JOIN</code> 的别名是 <code>TIDB_INLJ</code>，在 3.0.x 及之前版本仅支持使用该别名；之后的版本同时支持使用这两种名称，但推荐使用 <code>INL_JOIN</code>。</p></div></div></div><h3 id="no_index_joint1_name--tl_name-" style="position:relative">NO_INDEX_JOIN(t1_name [, tl_name ...])<a href="#no_index_joint1_name--tl_name-" aria-label="no_index_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_INDEX_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表不要使用 Index Nested Loop Join 算法。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_INDEX_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="inl_hash_join" style="position:relative">INL_HASH_JOIN<a href="#inl_hash_join" aria-label="inl_hash_join permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>INL_HASH_JOIN(t1_name [, tl_name])</code> 提示优化器使用 Index Nested Loop Hash Join 算法。该算法与 Index Nested Loop Join 使用条件完全一样，两者的区别是 <code>INL_JOIN</code> 会在连接的内表上建哈希表，而 <code>INL_HASH_JOIN</code> 会在连接的外表上建哈希表，后者对于内存的使用是有固定上限的，而前者使用的内存使用取决于内表匹配到的行数。</p><h3 id="no_index_hash_joint1_name--tl_name-" style="position:relative">NO_INDEX_HASH_JOIN(t1_name [, tl_name ...])<a href="#no_index_hash_joint1_name--tl_name-" aria-label="no_index_hash_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_INDEX_HASH_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表不要使用 Index Nested Loop Hash Join 算法。</p><h3 id="inl_merge_join" style="position:relative">INL_MERGE_JOIN<a href="#inl_merge_join" aria-label="inl_merge_join permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>INL_MERGE_JOIN(t1_name [, tl_name])</code> 提示优化器使用 Index Nested Loop Merge Join 算法，该算法与 Index Nested Loop Join 使用条件完全一样。</p><h3 id="no_index_merge_joint1_name--tl_name-" style="position:relative">NO_INDEX_MERGE_JOIN(t1_name [, tl_name ...])<a href="#no_index_merge_joint1_name--tl_name-" aria-label="no_index_merge_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_INDEX_MERGE_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表不要使用 Index Nested Loop Merge Join 算法。</p><h3 id="hash_joint1_name--tl_name-" style="position:relative">HASH_JOIN(t1_name [, tl_name ...])<a href="#hash_joint1_name--tl_name-" aria-label="hash_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>HASH_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Hash Join 算法。这个算法多线程并发执行，执行速度较快，但会消耗较多内存。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>HASH_JOIN</code> 的别名是 <code>TIDB_HJ</code>，在 3.0.x 及之前版本仅支持使用该别名；之后的版本同时支持使用这两种名称，推荐使用 <code>HASH_JOIN</code>。</p></div></div></div><h3 id="no_hash_joint1_name--tl_name-" style="position:relative">NO_HASH_JOIN(t1_name [, tl_name ...])<a href="#no_hash_joint1_name--tl_name-" aria-label="no_hash_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_HASH_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表不要使用 Hash Join 算法。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_HASH_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="hash_join_buildt1_name--tl_name-" style="position:relative">HASH_JOIN_BUILD(t1_name [, tl_name ...])<a href="#hash_join_buildt1_name--tl_name-" aria-label="hash_join_buildt1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>HASH_JOIN_BUILD(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Hash Join 算法，同时将指定表作为 Hash Join 算法的 Build 端，即用指定表来构建哈希表。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN_BUILD(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="hash_join_probet1_name--tl_name-" style="position:relative">HASH_JOIN_PROBE(t1_name [, tl_name ...])<a href="#hash_join_probet1_name--tl_name-" aria-label="hash_join_probet1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>HASH_JOIN_PROBE(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Hash Join 算法，同时将指定表作为 Hash Join 算法的探测（Probe）端，即用指定表作为探测端来执行 Hash Join 算法。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_JOIN_PROBE(t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="semi_join_rewrite" style="position:relative">SEMI_JOIN_REWRITE()<a href="#semi_join_rewrite" aria-label="semi_join_rewrite permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>SEMI_JOIN_REWRITE()</code> 提示优化器将查询语句中的半连接 (Semi Join) 改写为普通的内连接。目前该 Hint 只作用于 <code>EXISTS</code> 子查询。</p><p>如果不使用该 Hint 进行改写，Semi Join 在选择 Hash Join 的执行方式时，只能够使用子查询构建哈希表，因此在子查询比外查询结果集大时，执行速度可能会不及预期。Semi Join 在选择 Index Join 的执行方式时，只能够使用外查询作为驱动表，因此在子查询比外查询结果集小时，执行速度可能会不及预期。</p><p>在使用了 <code>SEMI_JOIN_REWRITE()</code> 进行改写后，优化器便可以扩大选择范围，选择更好的执行方式。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 不使用 SEMI_JOIN_REWRITE() 进行改写</span> EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> <span class="hljs-keyword">EXISTS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-number">1</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t.a); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> <span class="hljs-operator">|</span> MergeJoin_9 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> semi <span class="hljs-keyword">join</span>, <span class="hljs-keyword">left</span> key:test.t.a, <span class="hljs-keyword">right</span> key:test.t1.a <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexReader_25(Build) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_24 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_24 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_23(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_22 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_22 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+---------+-----------+------------------------+---------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 使用 SEMI_JOIN_REWRITE() 进行改写</span> EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> <span class="hljs-keyword">EXISTS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SEMI_JOIN_REWRITE() */</span> <span class="hljs-number">1</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t.a); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_16 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:IndexReader_15, <span class="hljs-keyword">outer</span> key:test.t1.a, <span class="hljs-keyword">inner</span> key:test.t.a, equal cond:eq(test.t1.a, test.t.a) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─StreamAgg_39(Build) <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t1.a, funcs:firstrow(test.t1.a)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span>test.t1.a <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexReader_34 <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:idx(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:Selection_14 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Selection_14 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t.a)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexRangeScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">1.25</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:idx(a) <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t.a, test.t1.a)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+---------+-----------+------------------------+---------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>在上述例子中可以看到，在使用了 Hint 之后，TiDB 可以选择由表 <code>t1</code> 作为驱动表的 IndexJoin 的执行方式。</p><h3 id="shuffle_joint1_name--tl_name-" style="position:relative">SHUFFLE_JOIN(t1_name [, tl_name ...])<a href="#shuffle_joint1_name--tl_name-" aria-label="shuffle_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>SHUFFLE_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Shuffle Join 算法，该 Hint 只在 MPP 模式下生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SHUFFLE_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li>使用该 Hint 前，需要保证当前 TiDB 集群能够支持在查询中使用 TiFlash MPP 模式，具体细节见文档<a href="/zh/tidb/stable/use-tiflash-mpp-mode/">使用 TiFlash MPP 模式</a>。</li><li>该 Hint 能与 <a href="#hash_join_buildt1_name--tl_name-"><code>HASH_JOIN_BUILD</code> Hint</a> 和 <a href="#hash_join_probet1_name--tl_name-"><code>HASH_JOIN_PROBE</code> Hint</a> 组合使用，达到控制 Shuffle Join 算法的 Build 端和 Probe 端的作用。</li></ul></div></div></div><h3 id="broadcast_joint1_name--tl_name-" style="position:relative">BROADCAST_JOIN(t1_name [, tl_name ...])<a href="#broadcast_joint1_name--tl_name-" aria-label="broadcast_joint1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>BROADCAST_JOIN(t1_name [, tl_name ...])</code> 提示优化器对指定表使用 Broadcast Join 算法，该 Hint 只在 MPP 模式下生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ BROADCAST_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li>使用该 Hint 前，需要保证当前 TiDB 集群能够支持在查询中使用 TiFlash MPP 模式，具体细节见文档<a href="/zh/tidb/stable/use-tiflash-mpp-mode/">使用 TiFlash MPP 模式</a>。</li><li>该 Hint 能与 <a href="#hash_join_buildt1_name--tl_name-"><code>HASH_JOIN_BUILD</code> Hint</a> 和 <a href="#hash_join_probet1_name--tl_name-"><code>HASH_JOIN_PROBE</code> Hint</a> 组合使用，达到控制 Broadcast Join 算法的 Build 端和 Probe 端的作用。</li></ul></div></div></div><h3 id="no_decorrelate" style="position:relative">NO_DECORRELATE()<a href="#no_decorrelate" aria-label="no_decorrelate permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_DECORRELATE()</code> 提示优化器不要尝试解除指定查询块中对应子查询的关联。该 Hint 适用于包含关联列的 <code>EXISTS</code>、<code>IN</code>、<code>ANY</code>、<code>ALL</code>、<code>SOME</code> 和标量子查询，即关联子查询。</p><p>将该 Hint 写在一个查询块中后，对于该子查询和其外部查询块之间的关联列，优化器将不再尝试解除关联，而是始终使用 Apply 算子来执行查询。</p><p>默认情况下，TiDB 会尝试对关联子查询<a href="/zh/tidb/stable/correlated-subquery-optimization/">解除关联</a>，以达到更高的执行效率。但是在<a href="/zh/tidb/stable/correlated-subquery-optimization/#限制">一部分场景</a>下，解除关联反而会降低执行效率。这种情况下，可以使用该 Hint 来人工提示优化器不要进行解除关联操作。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> t1(a <span class="hljs-type">int</span>, b <span class="hljs-type">int</span>); <span class="hljs-keyword">create</span> <span class="hljs-keyword">table</span> t2(a <span class="hljs-type">int</span>, b <span class="hljs-type">int</span>, index idx(b)); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 不使用 NO_DECORRELATE()</span> explain <span class="hljs-keyword">select</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&lt;</span> (<span class="hljs-keyword">select</span> <span class="hljs-built_in">sum</span>(t2.a) <span class="hljs-keyword">from</span> t2 <span class="hljs-keyword">where</span> t2.b <span class="hljs-operator">=</span> t1.b); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_11 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.b, test.t2.b)], other cond:lt(<span class="hljs-built_in">cast</span>(test.t1.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>), <span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─HashAgg_23(Build) <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t2.b, funcs:<span class="hljs-built_in">sum</span>(<span class="hljs-keyword">Column</span>#<span class="hljs-number">8</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>, funcs:firstrow(test.t2.b)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span>test.t2.b <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_24 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:HashAgg_16 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─HashAgg_16 <span class="hljs-operator">|</span> <span class="hljs-number">7992.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span>:test.t2.b, funcs:<span class="hljs-built_in">sum</span>(test.t2.a)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">8</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─Selection_22 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t2.b)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:Selection_14 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Selection_14 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">not</span>(isnull(test.t1.b)) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+----------+-----------+---------------+--------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>从以上执行计划中可以发现，优化器自动解除了关联。解除关联之后的执行计划不包含 Apply 算子，取而代之的是子查询和外部查询块之间的 Join 运算，而原本的带有关联列的过滤条件 <code>t2.b = t1.b</code> 也变成了一个普通的 join 条件。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 使用 NO_DECORRELATE()</span> explain <span class="hljs-keyword">select</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">from</span> t1 <span class="hljs-keyword">where</span> t1.a <span class="hljs-operator">&lt;</span> (<span class="hljs-keyword">select</span> <span class="hljs-comment">/*+ NO_DECORRELATE() */</span> <span class="hljs-built_in">sum</span>(t2.a) <span class="hljs-keyword">from</span> t2 <span class="hljs-keyword">where</span> t2.b <span class="hljs-operator">=</span> t1.b); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Projection_10 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.a, test.t1.b <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Apply_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> CARTESIAN <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, other cond:lt(<span class="hljs-built_in">cast</span>(test.t1.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>), <span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_14(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─MaxOneRow_15(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─StreamAgg_20 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> funcs:<span class="hljs-built_in">sum</span>(<span class="hljs-keyword">Column</span>#<span class="hljs-number">14</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">7</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_45 <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-built_in">cast</span>(test.t2.a, <span class="hljs-type">decimal</span>(<span class="hljs-number">10</span>,<span class="hljs-number">0</span>) <span class="hljs-type">BINARY</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">14</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexLookUp_44 <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexRangeScan_42(Build) <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2, index:idx(b) <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t2.b, test.t1.b)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRowIDScan_43(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">100000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------------------+-----------+-----------+------------------------+--------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>从以上执行计划中可以发现，优化器没有解除关联。执行计划中包含 Apply 算子，而带有关联列的条件 <code>t2.b = t1.b</code> 仍然是访问 <code>t2</code> 表时的过滤条件。</p><h3 id="hash_agg" style="position:relative">HASH_AGG()<a href="#hash_agg" aria-label="hash_agg permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>HASH_AGG()</code> 提示优化器对指定查询块中所有聚合函数使用 Hash Aggregation 算法。这个算法多线程并发执行，执行速度较快，但会消耗较多内存。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ HASH_AGG() */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="stream_agg" style="position:relative">STREAM_AGG()<a href="#stream_agg" aria-label="stream_agg permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>STREAM_AGG()</code> 提示优化器对指定查询块中所有聚合函数使用 Stream Aggregation 算法。这个算法通常会占用更少的内存，但执行时间会更久。数据量太大，或系统内存不足时，建议尝试使用。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ STREAM_AGG() */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="mpp_1phase_agg" style="position:relative">MPP_1PHASE_AGG()<a href="#mpp_1phase_agg" aria-label="mpp_1phase_agg permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>MPP_1PHASE_AGG()</code> 提示优化器对指定查询块中所有聚合函数使用一阶段聚合算法，该 Hint 只在 MPP 模式下生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MPP_1PHASE_AGG() */</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>使用该 Hint 前，需要保证当前 TiDB 集群能够支持在查询中使用 TiFlash MPP 模式，具体细节见文档<a href="/zh/tidb/stable/use-tiflash-mpp-mode/">使用 TiFlash MPP 模式</a>。</p></div></div></div><h3 id="mpp_2phase_agg" style="position:relative">MPP_2PHASE_AGG()<a href="#mpp_2phase_agg" aria-label="mpp_2phase_agg permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>MPP_2PHASE_AGG()</code> 提示优化器对指定查询块中所有聚合函数使用二阶段聚合算法，该 Hint 只在 MPP 模式下生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MPP_2PHASE_AGG() */</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> t1.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>使用该 Hint 前，需要保证当前 TiDB 集群能够支持在查询中使用 TiFlash MPP 模式，具体细节见文档<a href="/zh/tidb/stable/use-tiflash-mpp-mode/">使用 TiFlash MPP 模式</a>。</p></div></div></div><h3 id="use_indext1_name-idx1_name--idx2_name-" style="position:relative">USE_INDEX(t1_name, idx1_name [, idx2_name ...])<a href="#use_indext1_name-idx1_name--idx2_name-" aria-label="use_indext1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>USE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器对指定表仅使用给出的索引。</p><p>下面例子的效果等价于 <code>SELECT * FROM t t1 use index(idx1, idx2);</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t1, idx1, idx2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>当该 Hint 中只指定表名，不指定索引名时，表示不考虑使用任何索引，而是选择全表扫。</p></div></div></div><h3 id="force_indext1_name-idx1_name--idx2_name-" style="position:relative">FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])<a href="#force_indext1_name-idx1_name--idx2_name-" aria-label="force_indext1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器对指定表仅使用给出的索引。</p><p><code>FORCE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 的使用方法、作用和 <code>USE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 相同。</p><p>以下四个查询语句的效果相同：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX(t, idx1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ FORCE_INDEX(t, idx1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t use index(idx1); <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t force index(idx1); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="ignore_indext1_name-idx1_name--idx2_name-" style="position:relative">IGNORE_INDEX(t1_name, idx1_name [, idx2_name ...])<a href="#ignore_indext1_name-idx1_name--idx2_name-" aria-label="ignore_indext1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>IGNORE_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器对指定表忽略给出的索引。</p><p>下面例子的效果等价于 <code>SELECT * FROM t t1 ignore index(idx1, idx2);</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ IGNORE_INDEX(t1, idx1, idx2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="order_indext1_name-idx1_name--idx2_name-" style="position:relative">ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])<a href="#order_indext1_name-idx1_name--idx2_name-" aria-label="order_indext1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器对指定表仅使用给出的索引，并且按顺序读取指定的索引。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardError MuiAlert-standard css-kdwypz" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ErrorOutlineIcon"><path d="M11 15h2v2h-2zm0-8h2v6h-2zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">警告</div><p>这个 hint 有可能会导致 SQL 语句报错，建议先进行测试。如果测试时发生报错，请移除该 Hint。如果测试时运行正常，则可以继续使用。</p></div></div></div><p>此 hint 通常应用在下面这种场景中：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t(a <span class="hljs-type">INT</span>, b <span class="hljs-type">INT</span>, key(a), key(b)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ ORDER_INDEX(t, a) */</span> a <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> a LIMIT <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> <span class="hljs-operator">|</span> Limit_10 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_14 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:Limit_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Limit_13 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:a(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">true</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+---------+-----------+---------------------+-------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>优化器对该查询会生成两类计划：<code>Limit + IndexScan(keep order: true)</code> 和 <code>TopN + IndexScan(keep order: false)</code>，当使用了 <code>ORDER_INDEX</code> Hint，优化器会选择前一种按照顺序读取索引的计划。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li><p>如果查询本身并不需要按顺序读取索引，即在不使用 Hint 的前提下，优化器在任何情况下都不会生成按顺序读取索引的计划。此时，如果指定了 <code>ORDER_INDEX</code> Hint，会出现报错 <code>Can't find a proper physical plan for this query</code>，此时应考虑移除对应的 <code>ORDER_INDEX</code> Hint。</p></li><li><p>分区表上的索引无法支持按顺序读取，所以不应该对分区表及其相关的索引使用 <code>ORDER_INDEX</code> Hint。</p></li></ul></div></div></div><h3 id="no_order_indext1_name-idx1_name--idx2_name-" style="position:relative">NO_ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])<a href="#no_order_indext1_name-idx1_name--idx2_name-" aria-label="no_order_indext1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_ORDER_INDEX(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器对指定表仅使用给出的索引，并且不按顺序读取指定的索引。通常应用在下面这种场景中:</p><p>以下示例中查询语句的效果等价于 <code>SELECT * FROM t t1 use index(idx1, idx2);</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t(a <span class="hljs-type">INT</span>, b <span class="hljs-type">INT</span>, key(a), key(b)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_ORDER_INDEX(t, a) */</span> a <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> a LIMIT <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> <span class="hljs-operator">|</span> TopN_7 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t.a, <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_14 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:TopN_13 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TopN_13 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t.a, <span class="hljs-keyword">offset</span>:<span class="hljs-number">0</span>, count:<span class="hljs-number">10</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t, index:a(a) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------+----------+-----------+---------------------+--------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>和 <code>ORDER_INDEX</code> Hint 的示例相同，优化器对该查询会生成两类计划：<code>Limit + IndexScan(keep order: true)</code> 和 <code>TopN + IndexScan(keep order: false)</code>，当使用了 <code>NO_ORDER_INDEX</code> Hint，优化器会选择后一种不按照顺序读取索引的计划。</p><h3 id="agg_to_cop" style="position:relative">AGG_TO_COP()<a href="#agg_to_cop" aria-label="agg_to_cop permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>AGG_TO_COP()</code> 提示优化器将指定查询块中的聚合函数下推到 coprocessor。如果优化器没有下推某些适合下推的聚合函数，建议尝试使用。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ AGG_TO_COP() */</span> <span class="hljs-built_in">sum</span>(t1.a) <span class="hljs-keyword">FROM</span> t t1; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="limit_to_cop" style="position:relative">LIMIT_TO_COP()<a href="#limit_to_cop" aria-label="limit_to_cop permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>LIMIT_TO_COP()</code> 提示优化器将指定查询块中的 <code>Limit</code> 和 <code>TopN</code> 算子下推到 coprocessor。优化器没有下推 <code>Limit</code> 或者 <code>TopN</code> 算子时建议尝试使用该提示。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LIMIT_TO_COP() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> a <span class="hljs-operator">=</span> <span class="hljs-number">1</span> <span class="hljs-keyword">AND</span> b <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> c LIMIT <span class="hljs-number">1</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="read_from_storagetiflasht1_name--tl_name--tikvt2_name--tl_name-" style="position:relative">READ_FROM_STORAGE(TIFLASH[t1_name [, tl_name ...]], TIKV[t2_name [, tl_name ...]])<a href="#read_from_storagetiflasht1_name--tl_name--tikvt2_name--tl_name-" aria-label="read_from_storagetiflasht1_name tl_name tikvt2_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>READ_FROM_STORAGE(TIFLASH[t1_name [, tl_name ...]], TIKV[t2_name [, tl_name ...]])</code> 提示优化器从指定的存储引擎来读取指定的表，目前支持的存储引擎参数有 <code>TIKV</code> 和 <code>TIFLASH</code>。如果为表指定了别名，就只能使用表的别名作为 <code>READ_FROM_STORAGE()</code> 的参数；如果没有指定别名，则用表的本名作为其参数。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ READ_FROM_STORAGE(TIFLASH[t1], TIKV[t2]) */</span> t1.a <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.a; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="use_index_merget1_name-idx1_name--idx2_name-" style="position:relative">USE_INDEX_MERGE(t1_name, idx1_name [, idx2_name ...])<a href="#use_index_merget1_name-idx1_name--idx2_name-" aria-label="use_index_merget1_name idx1_name idx2_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>USE_INDEX_MERGE(t1_name, idx1_name [, idx2_name ...])</code> 提示优化器通过索引合并的方式来访问指定的表。索引合并分为并集型和交集型两种类型，详情参见<a href="/zh/tidb/stable/explain-index-merge/">用 EXPLAIN 查看索引合并的 SQL 执行计划</a>。</p><p>若显式地指定索引列表，优化器会尝试在索引列表中选取索引来构建索引合并。若不指定索引列表，优化器会尝试在所有可用的索引中选取索引来构建索引合并。</p><p>对于交集型索引合并，索引列表是必选参数。对于并集型索引合并，Hint 中的索引列表为可选参数。示例如下。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_INDEX_MERGE(t1, idx_a, idx_b, idx_c) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span> <span class="hljs-keyword">OR</span> t1.b <span class="hljs-operator">&gt;</span> <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>当对同一张表有多个 <code>USE_INDEX_MERGE</code> Hint 时，优化器会从这些 Hint 指定的索引列表的并集中尝试选取索引。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>USE_INDEX_MERGE</code> 的参数是索引名，而不是列名。对于主键索引，索引名为 <code>primary</code>。</p></div></div></div><h3 id="leadingt1_name--tl_name-" style="position:relative">LEADING(t1_name [, tl_name ...])<a href="#leadingt1_name--tl_name-" aria-label="leadingt1_name tl_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>LEADING(t1_name [, tl_name ...])</code> 提示优化器在生成多表连接的执行计划时，按照 hint 中表名出现的顺序来确定多表连接的顺序。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LEADING(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">and</span> t2.id <span class="hljs-operator">=</span> t3.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>在以上多表连接查询语句中，<code>LEADING()</code> 中表出现的顺序决定了优化器将会先对表 <code>t1</code> 和 <code>t2</code> 进行连接，再将结果和表 <code>t3</code> 进行连接。该 hint 比 <a href="#straight_join"><code>STRAIGHT_JOIN</code></a> 更为通用。</p><p><code>LEADING</code> hint 在以下情况下会失效：</p><ul><li>指定了多个 <code>LEADING</code> hint</li><li><code>LEADING</code> hint 中指定的表名不存在</li><li><code>LEADING</code> hint 中指定了重复的表名</li><li>优化器无法按照 <code>LEADING</code> hint 指定的顺序进行表连接</li><li>已经存在 <code>straight_join()</code> hint</li><li>查询语句中包含 outer join 且同时指定了包含笛卡尔积的情况</li></ul><p>当出现了上述失效的情况，会输出 warning 警告。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 指定了多个 LEADING hint</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ LEADING(t1, t2) LEADING(t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">and</span> t2.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-comment">-- 通过执行 `show warnings` 了解具体产生冲突的原因</span> <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> We can <span class="hljs-keyword">only</span> use <span class="hljs-keyword">one</span> <span class="hljs-keyword">leading</span> hint <span class="hljs-keyword">at</span> most, <span class="hljs-keyword">when</span> multiple <span class="hljs-keyword">leading</span> hints <span class="hljs-keyword">are</span> used, <span class="hljs-keyword">all</span> <span class="hljs-keyword">leading</span> hints will be invalid <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>如果查询语句中包含了 outer join，你只能在 hint 中指定可以用于交换连接顺序的表。如果 hint 中存在不能用于交换的表，则该 hint 会失效。例如在 <code>SELECT * FROM t1 LEFT JOIN (t2 JOIN t3 JOIN t4) ON t1.a = t2.a;</code> 中，如果想要控制 <code>t2</code>、<code>t3</code>、<code>t4</code> 表的连接顺序，那么在使用 <code>LEADING</code> hint 时，hint 中不能出现 <code>t1</code> 表。</p></div></div></div><h3 id="merge" style="position:relative">MERGE()<a href="#merge" aria-label="merge permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>在含有<a href="/zh/tidb/stable/dev-guide-use-common-table-expression/">公共表表达式</a>的查询中使用 <code>MERGE()</code> hint，可关闭对当前子查询的物化过程，并将内部查询的内联展开到外部查询。该 hint 适用于非递归的公共表表达式查询，在某些场景下，使用该 hint 会比默认分配一块临时空间的语句执行效率更高。例如将外部查询的条件下推或在嵌套的 CTE 查询中：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-comment">-- 使用 hint 将外部查询条件的谓词下推</span> <span class="hljs-keyword">WITH</span> CTE <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> tc <span class="hljs-keyword">WHERE</span> tc.a <span class="hljs-operator">&lt;</span> <span class="hljs-number">60</span>) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE <span class="hljs-keyword">WHERE</span> CTE.a <span class="hljs-operator">&lt;</span><span class="hljs-number">18</span>; <span class="hljs-comment">-- 在嵌套 CTE 查询中使用该 hint 来指定将某个 CTE 内联展开到外部查询</span> <span class="hljs-keyword">WITH</span> CTE1 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1), CTE2 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">WITH</span> CTE3 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t2), CTE4 <span class="hljs-keyword">AS</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t3) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE3, CTE4) <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> CTE1, CTE2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>MERGE()</code> 只适用于简单的 CTE 查询，在以下情况下无法使用该 hint：</p><ul><li><a href="/zh/tidb/stable/dev-guide-use-common-table-expression/#递归的-cte">递归的 CTE 查询</a></li><li>子查询中有无法进行内联展开的部分，例如聚合算子、窗口函数以及 <code>DINSTINCT</code> 等</li></ul><p>当 CTE 引用次数过多时，查询性能可能低于默认的物化方式。</p></div></div></div><h2 id="全局生效的-hint" style="position:relative">全局生效的 Hint<a href="#%E5%85%A8%E5%B1%80%E7%94%9F%E6%95%88%E7%9A%84-hint" aria-label="全局生效的 hint permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h2><p>全局生效的 Hint 和<a href="/zh/tidb/stable/views/">视图</a>有关，可以使查询中定义的 Hint 能够在视图内部生效。添加这类 Hint 需要两步：先用 <code>QB_NAME</code> Hint 为视图内的查询块命名，再以“视图名@查询块名”的方式加入实际需要的 Hint。</p><h3 id="第-1-步使用-qb_name-hint-重命名视图内的查询块" style="position:relative">第 1 步：使用 <code>QB_NAME</code> Hint 重命名视图内的查询块<a href="#%E7%AC%AC-1-%E6%AD%A5%E4%BD%BF%E7%94%A8-qb_name-hint-%E9%87%8D%E5%91%BD%E5%90%8D%E8%A7%86%E5%9B%BE%E5%86%85%E7%9A%84%E6%9F%A5%E8%AF%A2%E5%9D%97" aria-label="第 1 步使用 qb_name hint 重命名视图内的查询块 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>首先使用 <a href="#qb_name"><code>QB_NAME</code> Hint</a> 重命名视图内部的查询块。其中针对视图的 <code>QB_NAME</code> Hint 的概念与<a href="#qb_name">查询块范围生效的 <code>QB_NAME</code> Hint</a>相同，只是在语法上进行了相应的拓展。从 <code>QB_NAME(QB)</code> 拓展为 <code>QB_NAME(QB, 视图名@查询块名 [.视图名@查询块名 .视图名@查询块名 ...])</code>。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>@查询块名</code> 与后面紧跟的 <code>.视图名@查询块名</code> 部分之间需要有一个空格，否则 <code>.视图名@查询块名</code> 会被视作前面 <code>@查询块名</code> 的一部分。例如，<code>QB_NAME(v2_1, v2@SEL_1 .@SEL_1)</code> 不能写为 <code>QB_NAME(v2_1, v2@SEL_1.@SEL_1)</code>。</p></div></div></div><ul><li><p>对于单个视图、不包含子查询的简单语句，下面以重命名视图 <code>v</code> 的第一个查询块为例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* 注释：当前查询块的名字为默认的 @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> 对于视图 <code>v</code> 来说，从查询语句开始的首个视图是 <code>v@SEL_1</code>。视图 <code>v</code> 的第一个查询块可以声明为 <code>QB_NAME(v_1, v@SEL_1 .@SEL_1)</code>，也可以省略 <code>@SEL_1</code> 简写成 <code>QB_NAME(v_1, v)</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* 注释：当前查询块的名字为默认的 @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-comment">-- 使用全局生效的 Hint</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v_1, v) USE_INDEX(t@v_1, idx) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>对于嵌套视图和包含子查询的复杂语句，下面以重命名视图 <code>v1</code>、<code>v2</code> 的两个查询块为例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* 注释：当前查询块的名字为默认的 @SEL_1 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2 <span class="hljs-keyword">JOIN</span> ( <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/* 注释：当前查询块的名字为默认的 @SEL_2 */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2) vv; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> 对于第一个视图 <code>v2</code> 来说，从上面的语句开始的首个视图是 <code>v2@SEL_1</code>。对于第二个视图 <code>v2</code> 来说，首个视图表为 <code>v2@SEL_2</code>。下面的查询部分仅考虑第一个视图 <code>v2</code>。</p><p> 视图 <code>v2</code> 的第一个查询块可以声明为 <code>QB_NAME(v2_1, v2@SEL_1 .@SEL_1)</code>，视图 <code>v2</code> 的第二个查询块可以声明为 <code>QB_NAME(v2_2, v2@SEL_1 .@SEL_2)</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v2 <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">JOIN</span> <span class="hljs-comment">/* 注释：对于视图 v2 来说，当前查询块的名字为默认的 @SEL_1，因此当前查询块的视图列表是 v2@SEL_1 .@SEL_1 */</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">JOIN</span> v1 <span class="hljs-comment">/* 注释：对于视图 v2 来说，当前查询块的名字为默认的 @SEL_2，因此当前查询块的视图列表是 v2@SEL_1 .@SEL_2 */</span> ) tt; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p> 对于视图 <code>v1</code> 来说，从上面的语句开始的首个视图是 <code>v2@SEL_1 .v1@SEL_2</code>。视图 <code>v1</code> 的第一个查询块可以声明为 <code>QB_NAME(v1_1, v2@SEL_1 .v1@SEL_2 .@SEL_1)</code>，视图 <code>v1</code> 的第二个查询块可以声明为 <code>QB_NAME(v1_2, v2@SEL_1 .v1@SEL_2 .@SEL_2)</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">VIEW</span> v1 <span class="hljs-keyword">AS</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">JOIN</span> <span class="hljs-comment">/* 注释：对于视图 v1 来说，当前查询块的名字为默认的 @SEL_1，因此当前查询块的视图列表是 v2@SEL_1 .v1@SEL_2 .@SEL_1 */</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-built_in">COUNT</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">JOIN</span> t2 <span class="hljs-comment">/* 注释：对于视图 v1 来说，当前查询块的名字为默认的 @SEL_2，因此当前查询块的视图列表是 v2@SEL_1 .v1@SEL_2 .@SEL_2 */</span> ) tt; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li></ul><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li><p>与视图相关的全局生效的 Hint 必须先定义了对应的 <code>QB_NAME</code> Hint 才能使用。</p></li><li><p>使用一个 Hint 来指定视图内的多个表名时，需要保证在同一个 Hint 中出现的表名处于同一个视图的同一个查询块中。</p></li><li><p>对于最外层的查询来说，在定义和视图相关的 <code>QB_NAME</code> Hint 时：</p><ul><li>对于 <code>QB_NAME</code> Hint 中视图列表序列的第一项，在不显式声明 <code>@SEL_</code> 时，默认和定义 <code>QB_NAME</code> Hint 的查询块位置保持一致，即省略 <code>@SEL_</code> 的查询 <code>SELECT /*+ QB_NAME(qb1, v2) */ * FROM v2 JOIN (SELECT /*+ QB_NAME(qb2, v2) */ * FROM v2) vv;</code> 相当于 <code>SELECT /*+ QB_NAME(qb1, v2@SEL_1) */ * FROM v2 JOIN (SELECT /*+ QB_NAME(qb2, v2@SEL_2) */ * FROM v2) vv;</code>。</li><li>对于 <code>QB_NAME</code> Hint 中视图列表序列第一项之外的其他部分，只有 <code>@SEL_1</code> 可省略。即，如果声明处于当前部分的第一个查询块中，则 <code>@SEL_1</code> 可以省略，否则，不能省略 <code>@SEL_</code>。对于上面的例子：<ul><li>视图 <code>v2</code> 的第一个查询块可以声明为 <code>QB_NAME(v2_1, v2)</code></li><li>视图 <code>v2</code> 的第二个查询块可以声明为 <code>QB_NAME(v2_2, v2.@SEL_2)</code></li><li>视图 <code>v1</code> 的第一个查询块可以声明为 <code>QB_NAME(v1_1, v2.v1@SEL_2)</code></li><li>视图 <code>v1</code> 的第二个查询块可以声明为 <code>QB_NAME(v1_2, v2.v1@SEL_2 .@SEL_2)</code></li></ul></li></ul></li></ul></div></div></div><h3 id="第-2-步添加实际需要的-hint" style="position:relative">第 2 步：添加实际需要的 Hint<a href="#%E7%AC%AC-2-%E6%AD%A5%E6%B7%BB%E5%8A%A0%E5%AE%9E%E9%99%85%E9%9C%80%E8%A6%81%E7%9A%84-hint" aria-label="第 2 步添加实际需要的 hint permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>在定义好视图查询块部分的 <code>QB_NAME</code> Hint 后，你可以通过查询块的名字使用<a href="#%E6%9F%A5%E8%AF%A2%E5%9D%97%E8%8C%83%E5%9B%B4%E7%94%9F%E6%95%88%E7%9A%84-hint">查询块范围生效的 Hint</a>，以“视图名@查询块名”的方式加入实际需要的 Hint，使其在视图内部生效。例如：</p><ul><li><p>指定视图 <code>v2</code> 中第一个查询块的 <code>MERGE_JOIN()</code> Hint：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v2_1, v2) merge_join(t@v2_1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>指定视图 <code>v2</code> 中第二个查询块的 <code>MERGE_JOIN()</code> 和 <code>STREAM_AGG()</code> Hint：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v2_2, v2.@SEL_2) merge_join(t1@v2_2) stream_agg(@v2_2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>指定视图 <code>v1</code> 中第一个查询块的 <code>HASH_JOIN()</code> Hint：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v1_1, v2.v1@SEL_2) hash_join(t@v1_1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li><li><p>指定视图 <code>v1</code> 中第二个查询块的 <code>HASH_JOIN()</code> 和 <code>HASH_AGG()</code> Hint：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ QB_NAME(v1_2, v2.v1@SEL_2 .@SEL_2) hash_join(t1@v1_2) hash_agg(@v1_2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> v2; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></li></ul><h2 id="查询范围生效的-hint" style="position:relative">查询范围生效的 Hint<a href="#%E6%9F%A5%E8%AF%A2%E8%8C%83%E5%9B%B4%E7%94%9F%E6%95%88%E7%9A%84-hint" aria-label="查询范围生效的 hint permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h2><p>这类 Hint 只能跟在语句中<strong>第一个</strong> <code>SELECT</code>、<code>UPDATE</code> 或 <code>DELETE</code> 关键字的后面，等同于在当前这条查询运行时对指定的系统变量进行修改，其优先级高于现有系统变量的值。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>这类 Hint 虽然也有隐藏的可选变量 <code>@QB_NAME</code>，但就算指定了该值，Hint 还是会在整个查询范围生效。</p></div></div></div><h3 id="no_index_merge" style="position:relative">NO_INDEX_MERGE()<a href="#no_index_merge" aria-label="no_index_merge permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NO_INDEX_MERGE()</code> 会关闭优化器的 index merge 功能。</p><p>下面的例子不会使用 index merge：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_INDEX_MERGE() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t <span class="hljs-keyword">WHERE</span> t.a <span class="hljs-operator">&gt;</span> <span class="hljs-number">0</span> <span class="hljs-keyword">or</span> t.b <span class="hljs-operator">&gt;</span> <span class="hljs-number">0</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 Hint 外，系统变量 <code>tidb_enable_index_merge</code> 也能决定是否开启该功能。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li><code>NO_INDEX_MERGE</code> 优先级高于 <code>USE_INDEX_MERGE</code>，当这两类 Hint 同时存在时，<code>USE_INDEX_MERGE</code> 不会生效。</li><li>当存在子查询时，<code>NO_INDEX_MERGE</code> 放在最外层才能生效。</li></ul></div></div></div><h3 id="use_tojaboolean_value" style="position:relative">USE_TOJA(boolean_value)<a href="#use_tojaboolean_value" aria-label="use_tojaboolean_value permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>参数 <code>boolean_value</code> 可以是 <code>TRUE</code> 或者 <code>FALSE</code>。<code>USE_TOJA(TRUE)</code> 会开启优化器尝试将 in (subquery) 条件转换为 join 和 aggregation 的功能。相对地，<code>USE_TOJA(FALSE)</code> 会关闭该功能。</p><p>下面的例子会将 <code>in (SELECT t2.a FROM t2) subq</code> 转换为等价的 join 和 aggregation：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ USE_TOJA(TRUE) */</span> t1.a, t1.b <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-keyword">in</span> (<span class="hljs-keyword">SELECT</span> t2.a <span class="hljs-keyword">FROM</span> t2) subq; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 Hint 外，系统变量 <code>tidb_opt_insubq_to_join_and_agg</code> 也能决定是否开启该功能。</p><h3 id="max_execution_timen" style="position:relative">MAX_EXECUTION_TIME(N)<a href="#max_execution_timen" aria-label="max_execution_timen permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>MAX_EXECUTION_TIME(N)</code> 把语句的执行时间限制在 <code>N</code> 毫秒以内，超时后服务器会终止这条语句的执行。</p><p>下面的 Hint 设置了 1000 毫秒（即 1 秒）超时：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MAX_EXECUTION_TIME(1000) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1 <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span> t2 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 Hint 之外，系统变量 <code>global.max_execution_time</code> 也能对语句执行时间进行限制。</p><h3 id="memory_quotan" style="position:relative">MEMORY_QUOTA(N)<a href="#memory_quotan" aria-label="memory_quotan permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>MEMORY_QUOTA(N)</code> 用于限制语句执行时的内存使用。该 Hint 支持 MB 和 GB 两种单位。内存使用超过该限制时会根据当前设置的内存超限行为来打出一条 log 或者终止语句的执行。</p><p>下面的 Hint 设置了 1024 MB 的内存限制：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ MEMORY_QUOTA(1024 MB) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 Hint 外，系统变量 <a href="/zh/tidb/stable/system-variables/#tidb_mem_quota_query"><code>tidb_mem_quota_query</code></a> 也能限制语句执行的内存使用。</p><h3 id="read_consistent_replica" style="position:relative">READ_CONSISTENT_REPLICA()<a href="#read_consistent_replica" aria-label="read_consistent_replica permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>READ_CONSISTENT_REPLICA()</code> 会开启从数据一致的 TiKV follower 节点读取数据的特性。</p><p>下面的例子会从 follower 节点读取数据：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ READ_CONSISTENT_REPLICA() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 Hint 外，环境变量 <code>tidb_replica_read</code> 设为 <code>'follower'</code> 或者 <code>'leader'</code> 也能决定是否开启该特性。</p><h3 id="ignore_plan_cache" style="position:relative">IGNORE_PLAN_CACHE()<a href="#ignore_plan_cache" aria-label="ignore_plan_cache permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>IGNORE_PLAN_CACHE()</code> 提示优化器在处理当前 <code>prepare</code> 语句时不使用 plan cache。</p><p>该 Hint 用于在 <a href="/zh/tidb/stable/sql-prepared-plan-cache/">Prepared Plan Cache</a> 开启的场景下临时对某类查询禁用 plan cache。</p><p>以下示例强制该 <code>prepare</code> 语句不使用 plan cache：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">prepare</span> stmt <span class="hljs-keyword">FROM</span> <span class="hljs-string">'SELECT /*+ IGNORE_PLAN_CACHE() */ * FROM t WHERE t.id = ?'</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="set_varvar_namevar_value" style="position:relative">SET_VAR(VAR_NAME=VAR_VALUE)<a href="#set_varvar_namevar_value" aria-label="set_varvar_namevar_value permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>SET_VAR(VAR_NAME=VAR_VALUE)</code> 允许在语句执行期间以 Hint 形式临时修改会话级系统变量的值。当语句执行完成后，系统变量将在当前会话中自动恢复为原始值。通过这个 Hint 可以修改一部分与优化器、执行器相关的系统变量行为。支持通过 <code>SET_VAR(VAR_NAME=VAR_VALUE)</code> Hint 修改的系统变量请查看<a href="/zh/tidb/stable/system-variables/">系统变量</a>。</p><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardError MuiAlert-standard css-kdwypz" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ErrorOutlineIcon"><path d="M11 15h2v2h-2zm0-8h2v6h-2zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">警告</div><ul><li>强烈建议不要利用此 Hint 修改没有明确支持的变量，这可能会引发不可预知的行为。</li><li>注意不要把 <code>SET_VAR</code> 写在子查询中，否则可能会不生效。详情请参考 <a href="#set_var-%E5%86%99%E5%9C%A8%E5%AD%90%E6%9F%A5%E8%AF%A2%E4%B8%AD%E4%B8%8D%E7%94%9F%E6%95%88"><code>SET_VAR</code> 写在子查询中不生效</a>。</li></ul></div></div></div><p>下面是一个使用示例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SET_VAR(MAX_EXECUTION_TIME=1234) */</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME; <span class="hljs-keyword">SELECT</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>执行上述 SQL，第一个查询返回的结果是 Hint 中设置的 <code>1234</code>，而不是变量 <code>MAX_EXECUTION_TIME</code> 的默认值。第二个查询会返回变量的默认值。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">1234</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="straight_join" style="position:relative">STRAIGHT_JOIN()<a href="#straight_join" aria-label="straight_join permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>STRAIGHT_JOIN()</code> 提示优化器在生成表连接顺序时按照表名在 <code>FROM</code> 子句中出现的顺序进行连接。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ STRAIGHT_JOIN() */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t t1, t t2 <span class="hljs-keyword">WHERE</span> t1.a <span class="hljs-operator">=</span> t2.a; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><ul><li><code>STRAIGHT_JOIN</code> 优先级高于 <code>LEADING</code>，当这两类 Hint 同时存在时，<code>LEADING</code> 不会生效。</li><li>建议使用 <code>LEADING</code> Hint，它比 <code>STRAIGHT_JOIN</code> Hint 更通用。</li></ul></div></div></div><h3 id="nth_plann" style="position:relative">NTH_PLAN(N)<a href="#nth_plann" aria-label="nth_plann permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>NTH_PLAN(N)</code> 提示优化器选用在物理优化阶段搜索到的第 <code>N</code> 个物理计划。<code>N</code> 必须是正整数。</p><p>如果指定的 <code>N</code> 超出了物理优化阶段的搜索范围，TiDB 会返回 warning，并根据不存在该 Hint 时一样的策略选择最优物理计划。</p><p>该 Hint 在启用 cascades planner 的情况下不会生效。</p><p>以下示例会强制优化器在物理阶段选择搜索到的第 3 个物理计划：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NTH_PLAN(3) */</span> <span class="hljs-built_in">count</span>(<span class="hljs-operator">*</span>) <span class="hljs-keyword">from</span> t <span class="hljs-keyword">where</span> a <span class="hljs-operator">&gt;</span> <span class="hljs-number">5</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p><code>NTH_PLAN(N)</code> 主要用于测试用途，并且在未来不保证其兼容性，请谨慎使用。</p></div></div></div><h3 id="resource_groupresource_group_name" style="position:relative">RESOURCE_GROUP(resource_group_name)<a href="#resource_groupresource_group_name" aria-label="resource_groupresource_group_name permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>RESOURCE_GROUP(resource_group_name)</code> 用于<a href="/zh/tidb/stable/tidb-resource-control-ru-groups/">使用资源管控 (Resource Control) 实现资源组限制和流控</a>。此 Hint 将临时使用指定的资源组执行当前的语句。如果指定的资源组不存在，则该 Hint 将被忽略。</p><p>示例：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ RESOURCE_GROUP(rg1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t limit <span class="hljs-number">10</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-1bzshic" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="InfoOutlinedIcon"><path d="M11,9H13V7H11M12,20C7.59,20 4,16.41 4,12C4,7.59 7.59,4 12,4C16.41,4 20,7.59 20, 12C20,16.41 16.41,20 12,20M12,2A10,10 0 0,0 2,12A10,10 0 0,0 12,22A10,10 0 0,0 22,12A10, 10 0 0,0 12,2M11,17H13V11H11V17Z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">注意</div><p>自 v8.2.0 版本开始，TiDB 为此 Hint 引入权限控制。当系统变量 <a href="/zh/tidb/stable/system-variables/#tidb_resource_control_strict_mode-从-v820-版本开始引入"><code>tidb_resource_control_strict_mode</code></a> 设置为 <code>ON</code> 时，你需要有 <code>SUPER</code> 或者 <code>RESOURCE_GROUP_ADMIN</code> 或者 <code>RESOURCE_GROUP_USER</code> 权限才能使用此 Hint。如果没有所需权限，则此 Hint 会被忽略，同时 TiDB 会返回 warning，你可以在查询结束后通过 <code>SHOW WARNINGS;</code> 命令查看具体信息。</p></div></div></div><h2 id="常见-hint-不生效问题排查" style="position:relative">常见 Hint 不生效问题排查<a href="#%E5%B8%B8%E8%A7%81-hint-%E4%B8%8D%E7%94%9F%E6%95%88%E9%97%AE%E9%A2%98%E6%8E%92%E6%9F%A5" aria-label="常见 hint 不生效问题排查 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h2><h3 id="mysql-命令行客户端清除-hint-导致不生效" style="position:relative">MySQL 命令行客户端清除 Hint 导致不生效<a href="#mysql-%E5%91%BD%E4%BB%A4%E8%A1%8C%E5%AE%A2%E6%88%B7%E7%AB%AF%E6%B8%85%E9%99%A4-hint-%E5%AF%BC%E8%87%B4%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="mysql 命令行客户端清除 hint 导致不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>MySQL 命令行客户端在 5.7.7 版本之前默认清除了 Optimizer Hints。如果需要在这些早期版本的客户端中使用 Hint 语法，需要在启动客户端时加上 <code>--comments</code> 选项。例如 <code>mysql -h 127.0.0.1 -P 4000 -uroot --comments</code>。</p><h3 id="创建连接时不指定库名导致-hint-不生效" style="position:relative">创建连接时不指定库名导致 Hint 不生效<a href="#%E5%88%9B%E5%BB%BA%E8%BF%9E%E6%8E%A5%E6%97%B6%E4%B8%8D%E6%8C%87%E5%AE%9A%E5%BA%93%E5%90%8D%E5%AF%BC%E8%87%B4-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="创建连接时不指定库名导致 hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>如果创建连接时未指定数据库名，则可能出现 Hint 失效的情况。例如：</p><p>使用 <code>mysql -h127.0.0.1 -P4000 -uroot</code> 命令连接数据库时，未使用 <code>-D</code> 参数指定数据库名。然后执行下面的 SQL 语句：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ use_index(t, a) */</span> a <span class="hljs-keyword">FROM</span> test.t; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>由于无法识别表 <code>t</code> 对应的数据库名，因此 <code>use_index(t, a)</code> Hint 无法生效。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> use_index(.t, a) <span class="hljs-keyword">is</span> inapplicable, <span class="hljs-keyword">check</span> whether the <span class="hljs-keyword">table</span>(.t) <span class="hljs-keyword">exists</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="跨库查询不指定库名导致-hint-不生效" style="position:relative">跨库查询不指定库名导致 Hint 不生效<a href="#%E8%B7%A8%E5%BA%93%E6%9F%A5%E8%AF%A2%E4%B8%8D%E6%8C%87%E5%AE%9A%E5%BA%93%E5%90%8D%E5%AF%BC%E8%87%B4-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="跨库查询不指定库名导致 hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>对于跨库查询中需要访问的表，需要显式地指定数据库名，否则可能出现 Hint 失效的情况。例如执行下面跨库查询的 SQL 语句：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">USE test1; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1(a <span class="hljs-type">INT</span>, KEY(a)); USE test2; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2(a <span class="hljs-type">INT</span>, KEY(a)); <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ use_index(t1, a) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> test1.t1, t2; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>由于 <code>t1</code> 不在当前数据库 <code>test2</code> 下，因此 <code>use_index(t1, a)</code> Hint 无法被正确地识别。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> use_index(test2.t1, a) <span class="hljs-keyword">is</span> inapplicable, <span class="hljs-keyword">check</span> whether the <span class="hljs-keyword">table</span>(test2.t1) <span class="hljs-keyword">exists</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>此时，需要显式地指定库名，即将 <code>use_index(t1, a)</code> 修改为 <code>use_index(test1.t1, a)</code>。</p><h3 id="hint-位置不正确导致不生效" style="position:relative">Hint 位置不正确导致不生效<a href="#hint-%E4%BD%8D%E7%BD%AE%E4%B8%8D%E6%AD%A3%E7%A1%AE%E5%AF%BC%E8%87%B4%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="hint 位置不正确导致不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>如果没有按照 Optimizer Hints 语法将 Hint 正确地放在指定关键字的后面，它将无法生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-comment">/*+ use_index(t, a) */</span> <span class="hljs-keyword">FROM</span> t; <span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>Warning 信息如下：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1064</span> <span class="hljs-operator">|</span> You have an error <span class="hljs-keyword">in</span> your <span class="hljs-keyword">SQL</span> syntax; <span class="hljs-keyword">check</span> the manual that corresponds <span class="hljs-keyword">to</span> your TiDB version <span class="hljs-keyword">for</span> the <span class="hljs-keyword">right</span> syntax <span class="hljs-keyword">to</span> use [parser:<span class="hljs-number">8066</span>]Optimizer hint can <span class="hljs-keyword">only</span> be followed <span class="hljs-keyword">by</span> certain keywords <span class="hljs-keyword">like</span> <span class="hljs-keyword">SELECT</span>, <span class="hljs-keyword">INSERT</span>, etc. <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>在上面的示例中，你需要将 Hint 直接放在 <code>SELECT</code> 关键字之后。具体的语法规则参见 <a href="#%E8%AF%AD%E6%B3%95">Hint 语法</a>部分。</p><h3 id="inl_join-hint-不生效" style="position:relative"><code>INL_JOIN</code> Hint 不生效<a href="#inl_join-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="inl_join hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><h4 id="关联表的列上使用内置函数导致-inl_join-hint-不生效" style="position:relative">关联表的列上使用内置函数导致 <code>INL_JOIN</code> Hint 不生效<a href="#%E5%85%B3%E8%81%94%E8%A1%A8%E7%9A%84%E5%88%97%E4%B8%8A%E4%BD%BF%E7%94%A8%E5%86%85%E7%BD%AE%E5%87%BD%E6%95%B0%E5%AF%BC%E8%87%B4-inl_join-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="关联表的列上使用内置函数导致 inl_join hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h4><p>在某些情况下，如果在关联表的列上使用了内置函数，优化器可能无法选择 <code>IndexJoin</code> 计划，导致 <code>INL_JOIN</code> Hint 也无法生效。</p><p>例如，以下查询在关联表的列 <code>tname</code> 上使用了内置函数 <code>substr</code>：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (id <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>) <span class="hljs-keyword">primary</span> key, tname <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>)); <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (id <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>) <span class="hljs-keyword">primary</span> key, tname <span class="hljs-type">varchar</span>(<span class="hljs-number">10</span>)); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id<span class="hljs-operator">=</span>t2.id <span class="hljs-keyword">and</span> SUBSTR(t1.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>)<span class="hljs-operator">=</span>SUBSTR(t2.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>查询计划输出结果如下：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_12 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.id, test.t2.id) eq(<span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span>, <span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span>)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─Projection_17(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t2.id, test.t2.tname, substr(test.t2.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_19 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_18 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_18 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_14(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.tname, substr(test.t1.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_16 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_15 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableFullScan_15 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+----------+-----------+---------------+-----------------------------------------------------------------------+</span> <span class="hljs-number">7</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span>, <span class="hljs-number">1</span> warning (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SHOW</span> WARNINGS; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+---------+------+------------------------------------------------------------------------------------+ | Level | Code | Message | +---------+------+------------------------------------------------------------------------------------+ | Warning | 1815 | Optimizer Hint /*+ INL_JOIN(t1, t2) */ or /*+ TIDB_INLJ(t1, t2) */ is inapplicable | +---------+------+------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>从该示例中可以看到，<code>INL_JOIN</code> Hint 没有生效。该问题的根本原因是优化器限制导致无法使用 <code>Projection</code> 或者 <code>Selection</code> 算子作为 <code>IndexJoin</code> 的探测 (Probe) 端。</p><p>从 TiDB v8.0.0 起，你通过设置 <a href="/zh/tidb/stable/system-variables/#tidb_enable_inl_join_inner_multi_pattern-从-v700-版本开始引入"><code>tidb_enable_inl_join_inner_multi_pattern</code></a> 为 <code>ON</code> 来避免该问题。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> @<span class="hljs-variable">@tidb</span>_enable_inl_join_inner_multi_pattern<span class="hljs-operator">=</span><span class="hljs-keyword">ON</span>; Query OK, <span class="hljs-number">0</span> <span class="hljs-keyword">rows</span> affected (<span class="hljs-number">0.00</span> sec) EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ INL_JOIN(t1, t2) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.id<span class="hljs-operator">=</span>t2.id <span class="hljs-keyword">AND</span> SUBSTR(t1.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>)<span class="hljs-operator">=</span>SUBSTR(t2.tname,<span class="hljs-number">1</span>,<span class="hljs-number">2</span>); <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_18 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:Projection_14, <span class="hljs-keyword">outer</span> key:test.t1.id, <span class="hljs-keyword">inner</span> key:test.t2.id, equal cond:eq(<span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span>, <span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span>), eq(test.t1.id, test.t2.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─Projection_32(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.tname, substr(test.t1.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_34 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Projection_14(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">100000000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t2.id, test.t2.tname, substr(test.t2.tname, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>)<span class="hljs-operator">-</span><span class="hljs-operator">&gt;</span><span class="hljs-keyword">Column</span>#<span class="hljs-number">6</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_13 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [eq(test.t2.id, test.t1.id)], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------------------------+--------------+-----------+---------------+--------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">7</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h4 id="排序规则不兼容导致-inl_join-hintinl_hash_join-hintinl_merge_join-hint-不生效" style="position:relative">排序规则不兼容导致 <code>INL_JOIN</code> Hint、<code>INL_HASH_JOIN</code> Hint、<code>INL_MERGE_JOIN</code> Hint 不生效<a href="#%E6%8E%92%E5%BA%8F%E8%A7%84%E5%88%99%E4%B8%8D%E5%85%BC%E5%AE%B9%E5%AF%BC%E8%87%B4-inl_join-hintinl_hash_join-hintinl_merge_join-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="排序规则不兼容导致 inl_join hintinl_hash_join hintinl_merge_join hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h4><p>如果两个表的 Join key 的排序规则不能兼容，将无法使用 IndexJoin 来执行查询。此时 <a href="#inl_joint1_name--tl_name-"><code>INL_JOIN</code> Hint</a>、<a href="#inl_hash_join"><code>INL_HASH_JOIN</code> Hint</a>、<a href="#inl_merge_join"><code>INL_MERGE_JOIN</code> Hint</a> 将无法生效。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (k <span class="hljs-type">varchar</span>(<span class="hljs-number">8</span>), key(k)) <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_general_ci; <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (k <span class="hljs-type">varchar</span>(<span class="hljs-number">8</span>), key(k)) <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_bin; EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ tidb_inlj(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.k<span class="hljs-operator">=</span>t2.k; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>查询计划输出结果如下：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-operator">|</span> HashJoin_19 <span class="hljs-operator">|</span> <span class="hljs-number">12487.50</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.k, test.t2.k)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexReader_24(Build) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_23 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─IndexFullScan_23 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2, index:k(k) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexReader_22(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> index:IndexFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexFullScan_21 <span class="hljs-operator">|</span> <span class="hljs-number">9990.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1, index:k(k) <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------------+----------+-----------+----------------------+----------------------------------------------+</span> <span class="hljs-number">5</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span>, <span class="hljs-number">1</span> warning (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>上面的 SQL 语句中 <code>t1.k</code> 和 <code>t2.k</code> 的排序规则不能相互兼容（分别为 <code>utf8mb4_general_ci</code> 和 <code>utf8mb4_bin</code>），导致 IndexJoin 无法适用。因此 <code>INL_JOIN</code> 或 <code>TIDB_INLJ</code> Hint 也无法生效。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SHOW</span> WARNINGS; <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Level <span class="hljs-operator">|</span> Code <span class="hljs-operator">|</span> Message <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Warning <span class="hljs-operator">|</span> <span class="hljs-number">1815</span> <span class="hljs-operator">|</span> Optimizer Hint <span class="hljs-comment">/*+ INL_JOIN(t1) */</span> <span class="hljs-keyword">or</span> <span class="hljs-comment">/*+ TIDB_INLJ(t1) */</span> <span class="hljs-keyword">is</span> inapplicable <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------+------+----------------------------------------------------------------------------+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h4 id="连接顺序导致-inl_join-hint-不生效" style="position:relative">连接顺序导致 <code>INL_JOIN</code> Hint 不生效<a href="#%E8%BF%9E%E6%8E%A5%E9%A1%BA%E5%BA%8F%E5%AF%BC%E8%87%B4-inl_join-hint-%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="连接顺序导致 inl_join hint 不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h4><p><a href="#inl_joint1_name--tl_name-"><code>INL_JOIN(t1, t2)</code></a> 或 <code>TIDB_INLJ(t1, t2)</code> 的语义是让 <code>t1</code> 和 <code>t2</code> 作为 <code>IndexJoin</code> 的内表与其他表进行连接，而不是直接将 <code>t1</code> 和 <code>t2</code> 进行 <code>IndexJoin</code> 连接。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ inl_join(t1, t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id <span class="hljs-keyword">AND</span> t1.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> IndexJoin_16 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_13, <span class="hljs-keyword">outer</span> key:test.t2.id, test.t1.id, <span class="hljs-keyword">inner</span> key:test.t3.id, test.t3.id, equal cond:eq(test.t1.id, test.t3.id), eq(test.t2.id, test.t3.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexJoin_34(Build) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_31, <span class="hljs-keyword">outer</span> key:test.t2.id, <span class="hljs-keyword">inner</span> key:test.t1.id, equal cond:eq(test.t2.id, test.t1.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ ├─TableReader_40(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_39 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ │ └─TableFullScan_39 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableReader_31(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_30 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableRangeScan_30 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t2.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_13(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_12 <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t3 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t2.id test.t1.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------+</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>在上面例子中，<code>t1</code> 和 <code>t3</code> 并没有直接被一个 <code>IndexJoin</code> 连接起来。</p><p>如果想要直接使用 <code>IndexJoin</code> 来连接 <code>t1</code> 和 <code>t3</code>，需要先使用 <a href="#leadingt1_name--tl_name-"><code>LEADING</code> Hint</a> 指定 <code>t1</code> 和 <code>t3</code> 的连接顺序，然后再配合使用 <code>INL_JOIN</code>。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ leading(t1, t3), inl_join(t3) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2, t3 <span class="hljs-keyword">WHERE</span> t1.id <span class="hljs-operator">=</span> t2.id <span class="hljs-keyword">AND</span> t2.id <span class="hljs-operator">=</span> t3.id <span class="hljs-keyword">AND</span> t1.id <span class="hljs-operator">=</span> t3.id; <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> Projection_12 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test.t1.id, test.t1.name, test.t2.id, test.t2.name, test.t3.id, test.t3.name <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─HashJoin_21 <span class="hljs-operator">|</span> <span class="hljs-number">15625.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, equal:[eq(test.t1.id, test.t2.id) eq(test.t3.id, test.t2.id)] <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_36(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_35 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_35 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t2 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexJoin_28(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">12500.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">inner</span> <span class="hljs-keyword">join</span>, <span class="hljs-keyword">inner</span>:TableReader_25, <span class="hljs-keyword">outer</span> key:test.t1.id, <span class="hljs-keyword">inner</span> key:test.t3.id, equal cond:eq(test.t1.id, test.t3.id) <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─TableReader_34(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> │ └─TableFullScan_33 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t1 <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableReader_25(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> data:TableRangeScan_24 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRangeScan_24 <span class="hljs-operator">|</span> <span class="hljs-number">10000.00</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:t3 <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>: decided <span class="hljs-keyword">by</span> [test.t1.id], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">---------------------------------+----------+-----------+---------------+---------------------------------------------------------------------------------------------------------------------+</span> <span class="hljs-number">9</span> <span class="hljs-keyword">rows</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.01</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="使用-hint-导致错误-cant-find-a-proper-physical-plan-for-this-query" style="position:relative">使用 Hint 导致错误 <code>Can't find a proper physical plan for this query</code><a href="#%E4%BD%BF%E7%94%A8-hint-%E5%AF%BC%E8%87%B4%E9%94%99%E8%AF%AF-cant-find-a-proper-physical-plan-for-this-query" aria-label="使用 hint 导致错误 cant find a proper physical plan for this query permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p>在下面几种情况下，可能会出现 <code>Can't find a proper physical plan for this query</code> 错误：</p><ul><li>查询本身并不需要按顺序读取索引，即在不使用 Hint 的前提下，优化器在任何情况下都不会生成按顺序读取索引的计划。此时，如果指定了 <code>ORDER_INDEX</code> Hint，会出现此报错，此时应考虑移除对应的 <code>ORDER_INDEX</code> Hint。</li><li>查询使用了 <code>NO_JOIN</code> 相关的 Hint 排除了所有可能的 Join 方式。</li></ul><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (a <span class="hljs-type">INT</span>); <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (a <span class="hljs-type">INT</span>); EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_HASH_JOIN(t1), NO_MERGE_JOIN(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a<span class="hljs-operator">=</span>t2.a; ERROR <span class="hljs-number">1815</span> (HY000): Internal : Can<span class="hljs-string">'t find a proper physical plan for this query </span></div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><ul><li>系统变量 <a href="/zh/tidb/stable/system-variables/#tidb_opt_enable_hash_join-从-v656v712-和-v740-版本开始引入"><code>tidb_opt_enable_hash_join</code></a> 设置为 <code>OFF</code>，而且其他 Join 方式也都被排除了。</li></ul><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t1 (a <span class="hljs-type">INT</span>); <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> t2 (a <span class="hljs-type">INT</span>); <span class="hljs-keyword">set</span> tidb_opt_enable_hash_join<span class="hljs-operator">=</span>off; EXPLAIN <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ NO_MERGE_JOIN(t1) */</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t1, t2 <span class="hljs-keyword">WHERE</span> t1.a<span class="hljs-operator">=</span>t2.a; ERROR <span class="hljs-number">1815</span> (HY000): Internal : Can<span class="hljs-string">'t find a proper physical plan for this query </span></div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="set_var-写在子查询中不生效" style="position:relative"><code>SET_VAR</code> 写在子查询中不生效<a href="#set_var-%E5%86%99%E5%9C%A8%E5%AD%90%E6%9F%A5%E8%AF%A2%E4%B8%AD%E4%B8%8D%E7%94%9F%E6%95%88" aria-label="set_var 写在子查询中不生效 permalink" class="anchor after"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a></h3><p><code>SET_VAR</code> 用来设置当前语句的系统变量，不要写在子查询中。如果写在子查询中，由于子查询会被特殊处理，可能导致 <code>SET_VAR</code> 无法生效。</p><p>下面示例把 <code>SET_VAR</code> 写在了子查询中，所以没有生效。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SELECT</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME, a <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SET_VAR(MAX_EXECUTION_TIME=123) */</span> <span class="hljs-number">1</span> <span class="hljs-keyword">as</span> a) t; <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+---+</span> <span class="hljs-operator">|</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME <span class="hljs-operator">|</span> a <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+---+</span> <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> <span class="hljs-number">1</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+---+</span> <span class="hljs-number">1</span> <span class="hljs-type">row</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">set</span> (<span class="hljs-number">0.00</span> sec) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>下面示例没有把 SET_VAR 写在子查询中，所以可以生效。</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-comment">/*+ SET_VAR(MAX_EXECUTION_TIME=123) */</span> @<span class="hljs-variable">@MAX</span>_EXECUTION_TIME, a <span class="hljs-keyword">FROM</span> (<span class="hljs-keyword">SELECT</span> <span class="hljs-number">1</span> <span class="hljs-keyword">as</span> a) t; <span class="hljs-operator">+</span><span class="hljs-comment">----------------------+---+</span>