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8px;width:100%;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;cursor:pointer;-webkit-tap-highlight-color:transparent;}.css-khel7y:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-khel7y:hover{background-color:transparent;}}.css-khel7y.Mui-disabled{opacity:0.38;background-color:transparent;}.css-khel7y.Mui-focused{background-color:rgba(0, 0, 0, 0.12);}.css-khel7y.Mui-selected{background-color:rgba(25, 118, 210, 0.08);}.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.12);}@media (hover: none){.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.08);}}.css-khel7y.Mui-selected.Mui-focused{background-color:rgba(25, 118, 210, 0.2);}.css-khel7y .MuiTreeItem-iconContainer{margin-right:4px;width:15px;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;}.css-khel7y .MuiTreeItem-iconContainer svg{font-size:18px;}.css-khel7y .MuiTreeItem-label{width:100%;min-width:0;padding-left:4px;position:relative;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;}</style><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css znl8a3">.css-znl8a3{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;min-height:1.75rem;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;padding-left:0rem;padding-top:0.25rem;padding-bottom:0.25rem;}</style><div class="css-znl8a3"><style data-emotion="css tx8jsd">.css-tx8jsd{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;}</style><a class="MuiTypography-root MuiTypography-body1 css-tx8jsd" target="_blank" href="https://docs.pingcap.com/zh" style="text-decoration:none;width:100%;color:inherit"><style data-emotion="css 8atqhb">.css-8atqhb{width:100%;}</style><div class="MuiBox-root css-8atqhb"><style data-emotion="css 1hwyipb">.css-1hwyipb{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;color:inherit;font-size:0.875rem;line-height:1.25rem;}</style><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">文档中心</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">关于 TiDB</div></div><style data-emotion="css xjq79n">.css-xjq79n{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:1.5rem;fill:#999999;height:1rem;width:1rem;margin-left:auto;-webkit-transform:none;-moz-transform:none;-ms-transform:none;transform:none;}</style><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div><style data-emotion="css 1jozaee">.css-1jozaee{margin:0;padding:0;margin-left:17px;}</style></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">快速上手</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">应用开发</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-4" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">部署标准集群</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-5" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">数据迁移</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">数据集成</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">运维操作</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">监控与告警</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">故障诊断</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-10" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">性能调优</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">教程</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">TiDB 工具</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-13" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">参考指南</div></div><style data-emotion="css 171pefp">.css-171pefp{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:1.5rem;fill:#999999;height:1rem;width:1rem;margin-left:auto;-webkit-transform:rotate(90deg);-moz-transform:rotate(90deg);-ms-transform:rotate(90deg);transform:rotate(90deg);}</style><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-171pefp" 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></div></div><style data-emotion="css 1xxsnna">.css-1xxsnna{height:auto;overflow:visible;-webkit-transition:height 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:height 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;margin:0;padding:0;margin-left:17px;}</style><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-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css kb2j4b">.css-kb2j4b{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;min-height:1.75rem;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;padding-left:0.5rem;padding-top:0.25rem;padding-bottom:0.25rem;}</style><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">架构</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">存储引擎 TiKV</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">存储引擎 TiFlash</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/system-variables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">系统变量</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-4" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">配置文件参数</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-5" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">CLI</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">命令行参数</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">监控指标</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">安全加固</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">权限</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium 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MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/table-attributes"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">表属性</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-10-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">事务</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-10-10" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/views"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">视图</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-10-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a 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style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/cached-tables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">缓存表</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-10-14" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/foreign-key"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">外键约束</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-10-15" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">字符集和排序</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-10-16" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/placement-rules-in-sql"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Placement Rules in SQL</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-10-17" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">系统表</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-10-18" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/metadata-lock"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">元数据锁</div></div></a></div></div></div></li></div></div></ul></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">UI</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/telemetry"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">遥测</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-13" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/error-codes"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">错误码</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-14" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/schedule-replicas-by-topology-labels"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">通过拓扑 label 进行副本调度</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-15" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">内部组件介绍</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li></div></div></ul></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-14" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">常见问题解答 (FAQ)</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-15" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">版本发布历史</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" 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></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-16" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/glossary"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">术语表</div></div></a></div></div></div></li></ul></div></aside><style data-emotion="css sb2sd0">.css-sb2sd0{width:100%;}@media (min-width:1200px){.css-sb2sd0{max-width:calc(100% - 18.75rem);}}</style><main class="MuiBox-root css-sb2sd0"><style data-emotion="css 1rnnmjb">.css-1rnnmjb{max-width:1340px;width:100%;margin-left:auto;margin-right:auto;display:block;box-sizing:border-box;}</style><div class="MuiBox-root css-1rnnmjb"><style data-emotion="css 90fn5w">.css-90fn5w{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;}@media (min-width:0px){.css-90fn5w{-webkit-flex-direction:column-reverse;-ms-flex-direction:column-reverse;flex-direction:column-reverse;}}@media (min-width:600px){.css-90fn5w{-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;}}</style><div class="css-90fn5w"><style data-emotion="css vofosd">.css-vofosd{padding:1.5rem 0;}@media (min-width:0px){.css-vofosd{width:100%;}}@media (min-width:600px){.css-vofosd{width:calc(100% - 17.5rem);}}</style><div class="MuiBox-root css-vofosd"><style data-emotion="css 1ekb41w">.css-1ekb41w{width:100%;margin-left:auto;box-sizing:border-box;margin-right:auto;display:block;padding-left:16px;padding-right:16px;}@media (min-width:600px){.css-1ekb41w{padding-left:24px;padding-right:24px;}}@media (min-width:1536px){.css-1ekb41w{max-width:1536px;}}</style><div class="MuiContainer-root MuiContainer-maxWidthXl doc-content css-1ekb41w"><div class="markdown-body MuiBox-root css-0"><h1 id="约束" style="position:relative"><a href="#%E7%BA%A6%E6%9D%9F" aria-label="约束 permalink" class="anchor before"><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>约束</h1><p>TiDB 支持的约束与 MySQL 的基本相同。</p><h2 id="非空约束" style="position:relative"><a href="#%E9%9D%9E%E7%A9%BA%E7%BA%A6%E6%9D%9F" aria-label="非空约束 permalink" class="anchor before"><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>非空约束</h2><p>TiDB 支持的非空约束规则与 MySQL 支持的一致。例如：</p><pre><code class="language-sql">CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, age INT NOT NULL, last_login TIMESTAMP </code></pre><pre><code class="language-sql">INSERT INTO users (id,age,last_login) VALUES (NULL,123,NOW()); </code></pre><pre><code>Query OK, 1 row affected (0.02 sec) </code></pre><pre><code class="language-sql">INSERT INTO users (id,age,last_login) VALUES (NULL,NULL,NOW()); </code></pre><pre><code>ERROR 1048 (23000): Column 'age' cannot be null </code></pre><pre><code class="language-sql">INSERT INTO users (id,age,last_login) VALUES (NULL,123,NULL); </code></pre><pre><code>Query OK, 1 row affected (0.03 sec) </code></pre><ul><li><p>第一条 <code>INSERT</code> 语句成功，因为对于定义为 <code>AUTO_INCREMENT</code> 的列，允许 <code>NULL</code> 作为其特殊值。TiDB 将为其分配下一个自动值。</p></li><li><p>第二条 <code>INSERT</code> 语句失败，因为 <code>age</code> 列被定义为 <code>NOT NULL</code>。</p></li><li><p>第三条 <code>INSERT</code> 语句成功，因为 <code>last_login</code> 列没有被明确地指定为 <code>NOT NULL</code>。默认允许 <code>NULL</code> 值。</p></li></ul><h2 id="check-约束" style="position:relative"><a href="#check-%E7%BA%A6%E6%9D%9F" aria-label="check 约束 permalink" class="anchor before"><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><code>CHECK</code> 约束</h2><style data-emotion="css 1weqspv">.css-1weqspv{padding-top:0.5rem;padding-bottom:0.5rem;}.css-1weqspv .MuiAlert-message p{margin-bottom:0px;margin-top:0px;}</style><div class="MuiBox-root css-1weqspv"><style data-emotion="css 17zlexa">.css-17zlexa{font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(1, 67, 97);background-color:rgb(229, 246, 253);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-17zlexa .MuiAlert-icon{color:#03a9f4;}</style><style data-emotion="css 152gid5">.css-152gid5{background-color:#fff;color:rgba(0, 0, 0, 0.87);-webkit-transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:box-shadow 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;border-radius:4px;box-shadow:none;font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(1, 67, 97);background-color:rgb(229, 246, 253);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-152gid5 .MuiAlert-icon{color:#03a9f4;}</style><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" role="alert"><style data-emotion="css 1l54tgj">.css-1l54tgj{margin-right:12px;padding:7px 0;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;font-size:22px;opacity:0.9;}</style><div class="MuiAlert-icon css-1l54tgj"><style data-emotion="css 1cw4hi4">.css-1cw4hi4{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:inherit;}</style><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><style data-emotion="css 1xsto0d">.css-1xsto0d{padding:8px 0;min-width:0;overflow:auto;}</style><div class="MuiAlert-message css-1xsto0d"><style data-emotion="css 1h2y6o4">.css-1h2y6o4{font-weight:500;margin-top:-2px;}</style><style data-emotion="css 17ioyuk">.css-17ioyuk{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;margin-bottom:0.35em;font-weight:500;margin-top:-2px;}</style><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">注意</div><p><code>CHECK</code> 约束功能默认关闭，需要将变量 <a href="/zh/tidb/dev/system-variables#tidb_enable_check_constraint-从-v720-版本开始引入"><code>tidb_enable_check_constraint</code></a> 设置为 <code>ON</code> 后才能开启。</p></div></div></div><p><code>CHECK</code> 约束用于限制表中某个字段的值必须满足指定条件。当为表添加 <code>CHECK</code> 约束后，在插入或者更新表的数据时，TiDB 会检查约束条件是否满足，如果不满足，则会报错。</p><p>TiDB 中 <code>CHECK</code> 约束的语法如下，与 MySQL 中一致：</p><pre><code class="language-sql">[CONSTRAINT [symbol]] CHECK (expr) [[NOT] ENFORCED] </code></pre><p>语法说明：</p><ul><li><code>[]</code> 中的内容表示可选项。</li><li><code>CONSTRAINT [symbol]</code> 表示 <code>CHECK</code> 约束的名称。</li><li><code>CHECK (expr)</code> 表示约束条件，其中 <code>expr</code> 需要为一个布尔表达式。对于表中的每一行，该表达式的计算结果必须为 <code>TRUE</code>、<code>FALSE</code> 或 <code>UNKNOWN</code> (对于 <code>NULL</code> 值) 中的一个。对于某行数据，如果该表达式计算结果为 <code>FALSE</code>，则表示违反约束条件。</li><li><code>[NOT] ENFORCED</code> 表示是否执行约束，可以用于启用或者禁用 <code>CHECK</code> 约束。</li></ul><h3 id="添加-check-约束" style="position:relative"><a href="#%E6%B7%BB%E5%8A%A0-check-%E7%BA%A6%E6%9D%9F" aria-label="添加 check 约束 permalink" class="anchor before"><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>添加 <code>CHECK</code> 约束</h3><p>在 TiDB 中，你可以在 <a href="/zh/tidb/dev/sql-statement-create-table"><code>CREATE TABLE</code></a> 或者 <a href="/zh/tidb/dev/sql-statement-modify-column"><code>ALTER TABLE</code></a> 语句中为表添加 <code>CHECK</code> 约束。</p><ul><li><p>在 <code>CREATE TABLE</code> 语句中添加 <code>CHECK</code> 约束的示例：</p><pre><code class="language-sql">CREATE TABLE t(a INT CHECK(a &gt; 10) NOT ENFORCED, b INT, c INT, CONSTRAINT c1 CHECK (b &gt; c)); </code></pre></li><li><p>在 <code>ALTER TABLE</code> 语句中添加 <code>CHECK</code> 约束的示例：</p><pre><code class="language-sql">ALTER TABLE t ADD CONSTRAINT CHECK (1 &lt; c); </code></pre></li></ul><p>在添加或者启用 <code>CHECK</code> 约束时，TiDB 会对表中的存量数据进行校验。如果存在违反约束的数据，添加 <code>CHECK</code> 约束操作将失败并且报错。</p><p>在添加 <code>CHECK</code> 约束时，可以指定约束名，也可以不指定约束名。如果不指定约束名，那么 TiDB 会自动生成一个格式为 <code>&lt;tableName&gt;_chk_&lt;1, 2, 3...&gt;</code> 的约束名。</p><h3 id="查看-check-约束" style="position:relative"><a href="#%E6%9F%A5%E7%9C%8B-check-%E7%BA%A6%E6%9D%9F" aria-label="查看 check 约束 permalink" class="anchor before"><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>查看 <code>CHECK</code> 约束</h3><p>你可以通过 <a href="/zh/tidb/dev/sql-statement-show-create-table"><code>SHOW CREATE TABLE</code></a> 查看表中的约束信息。例如：</p><pre><code class="language-sql">SHOW CREATE TABLE t; +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | t | CREATE TABLE `t` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) DEFAULT NULL, CONSTRAINT `c1` CHECK ((`b` &gt; `c`)), CONSTRAINT `t_chk_1` CHECK ((`a` &gt; 10)) /*!80016 NOT ENFORCED */, CONSTRAINT `t_chk_2` CHECK ((1 &lt; `c`)) ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin | +-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) </code></pre><h3 id="删除-check-约束" style="position:relative"><a href="#%E5%88%A0%E9%99%A4-check-%E7%BA%A6%E6%9D%9F" aria-label="删除 check 约束 permalink" class="anchor before"><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>删除 <code>CHECK</code> 约束</h3><p>删除 <code>CHECK</code> 约束时，你需要指定需要删除的约束名。例如：</p><pre><code class="language-sql">ALTER TABLE t DROP CONSTRAINT t_chk_1; </code></pre><h3 id="启用或禁用-check-约束" style="position:relative"><a href="#%E5%90%AF%E7%94%A8%E6%88%96%E7%A6%81%E7%94%A8-check-%E7%BA%A6%E6%9D%9F" aria-label="启用或禁用 check 约束 permalink" class="anchor before"><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>启用或禁用 <code>CHECK</code> 约束</h3><p>在为表<a href="#%E6%B7%BB%E5%8A%A0-check-%E7%BA%A6%E6%9D%9F">添加 <code>CHECK</code> 约束</a>的时候，可以指定当插入或者更新数据时 TiDB 是否执行约束检查。</p><ul><li>如果指定了 <code>NOT ENFORCED</code>，当插入或者更新数据时，TiDB 不会检查约束条件。</li><li>如果未指定 <code>NOT ENFORCED</code> 或者指定了 <code>ENFORCED</code>，当插入或者更新数据时，TiDB 会检查约束条件。</li></ul><p>除了在添加约束时候指定 <code>[NOT] ENFORCED</code>，你还可以在 <code>ALTER TABLE</code> 语句中启用或者禁用 <code>CHECK</code> 约束。例如：</p><pre><code class="language-sql">ALTER TABLE t ALTER CONSTRAINT c1 NOT ENFORCED; </code></pre><h3 id="与-mysql-的兼容性" style="position:relative"><a href="#%E4%B8%8E-mysql-%E7%9A%84%E5%85%BC%E5%AE%B9%E6%80%A7" aria-label="与 mysql 的兼容性 permalink" class="anchor before"><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>与 MySQL 的兼容性</h3><ul><li>不支持在添加列的同时添加 <code>CHECK</code> 约束（例如，<code>ALTER TABLE t ADD COLUMN a CHECK(a &gt; 0)</code>)），否则只有列会被添加成功，TiDB 会忽略 <code>CHECK</code> 约束但不会报错。</li><li>不支持使用 <code>ALTER TABLE t CHANGE a b int CHECK(b &gt; 0)</code> 添加 <code>CHECK</code> 约束，使用该语句时 TiDB 会报错。</li></ul><h2 id="唯一约束" style="position:relative"><a href="#%E5%94%AF%E4%B8%80%E7%BA%A6%E6%9D%9F" aria-label="唯一约束 permalink" class="anchor before"><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>唯一约束</h2><p>唯一约束是指唯一索引和主键列中所有的非空值都是唯一的。</p><h3 id="乐观事务" style="position:relative"><a href="#%E4%B9%90%E8%A7%82%E4%BA%8B%E5%8A%A1" aria-label="乐观事务 permalink" class="anchor before"><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>乐观事务</h3><p>在 TiDB 的乐观事务中，默认会对唯一约束进行<a href="/zh/tidb/dev/transaction-overview#惰性检查">惰性检查</a>。通过在事务提交时再进行批量检查，TiDB 能够减少网络开销、提升性能。例如：</p><pre><code class="language-sql">DROP TABLE IF EXISTS users; CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, username VARCHAR(60) NOT NULL, UNIQUE KEY (username) INSERT INTO users (username) VALUES ('dave'), ('sarah'), ('bill'); </code></pre><p>乐观事务模式下且 <code>tidb_constraint_check_in_place=OFF</code>：</p><pre><code class="language-sql">BEGIN OPTIMISTIC; INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); </code></pre><pre><code>Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 </code></pre><pre><code class="language-sql">INSERT INTO users (username) VALUES ('steve'),('elizabeth'); </code></pre><pre><code>Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0 </code></pre><pre><code class="language-sql">COMMIT; </code></pre><pre><code>ERROR 1062 (23000): Duplicate entry 'bill' for key 'users.username' </code></pre><p>在以上乐观事务的示例中，唯一约束的检查推迟到事务提交时才进行。由于 <code>bill</code> 值已经存在，这一行为导致了重复键错误。</p><p>你可通过设置 <a href="/zh/tidb/dev/system-variables#tidb_constraint_check_in_place"><code>tidb_constraint_check_in_place</code></a> 为 <code>ON</code> 停用此行为（该变量仅适用于乐观事务，悲观事务需通过 <code>tidb_constraint_check_in_place_pessimistic</code> 设置）。当 <code>tidb_constraint_check_in_place</code> 设置为 <code>ON</code> 时，TiDB 会在执行语句时就对唯一约束进行检查。例如：</p><pre><code class="language-sql">DROP TABLE IF EXISTS users; CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, username VARCHAR(60) NOT NULL, UNIQUE KEY (username) INSERT INTO users (username) VALUES ('dave'), ('sarah'), ('bill'); </code></pre><pre><code class="language-sql">SET tidb_constraint_check_in_place = ON; </code></pre><pre><code>Query OK, 0 rows affected (0.00 sec) </code></pre><pre><code class="language-sql">BEGIN OPTIMISTIC; </code></pre><pre><code>Query OK, 0 rows affected (0.00 sec) </code></pre><pre><code class="language-sql">INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); </code></pre><pre><code>ERROR 1062 (23000): Duplicate entry 'bill' for key 'users.username' </code></pre><p>第一条 <code>INSERT</code> 语句导致了重复键错误。这会造成额外的网络通信开销，并可能降低插入操作的吞吐量。</p><h3 id="悲观事务" style="position:relative"><a href="#%E6%82%B2%E8%A7%82%E4%BA%8B%E5%8A%A1" aria-label="悲观事务 permalink" class="anchor before"><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>悲观事务</h3><p>在 TiDB 的悲观事务中，默认在执行任何一条需要插入或更新唯一索引的 SQL 语句时都会进行唯一约束检查：</p><pre><code class="language-sql">DROP TABLE IF EXISTS users; CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, username VARCHAR(60) NOT NULL, UNIQUE KEY (username) INSERT INTO users (username) VALUES ('dave'), ('sarah'), ('bill'); BEGIN PESSIMISTIC; INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); </code></pre><pre><code>ERROR 1062 (23000): Duplicate entry 'bill' for key 'users.username' </code></pre><p>对于悲观事务，你可以设置变量 <a href="/zh/tidb/dev/system-variables#tidb_constraint_check_in_place_pessimistic-从-v630-版本开始引入"><code>tidb_constraint_check_in_place_pessimistic</code></a> 为 <code>OFF</code> 来推迟唯一约束检查，到下一次对该唯一索引项加锁时或事务提交时再进行检查，同时也跳过对该悲观锁加锁，以获得更好的性能。此时需要注意：</p><ul><li><p>由于推迟了唯一约束检查，TiDB 可能会读取到不满足唯一约束的结果，执行 <code>COMMIT</code> 语句时可能返回 <code>Duplicate entry</code> 错误。返回该错误时，TiDB 会回滚当前事务。</p><p> 下面这个例子跳过了对 <code>bill</code> 的加锁，因此 TiDB 可能读到不满足唯一性约束的结果：</p><pre><code class="language-sql">SET tidb_constraint_check_in_place_pessimistic = OFF; BEGIN PESSIMISTIC; INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); -- Query OK, 3 rows affected SELECT * FROM users FOR UPDATE; </code></pre><p> TiDB 读到了不满足唯一性约束的结果：有两个 <code>bill</code>。</p><pre><code class="language-sql">+----+----------+ | id | username | +----+----------+ | 1 | dave | | 2 | sarah | | 3 | bill | | 7 | jane | | 8 | chris | | 9 | bill | +----+----------+ </code></pre><p> 此时，如果提交事务，TiDB 将进行唯一约束检查，报出 <code>Duplicate entry</code> 错误并回滚事务。</p><pre><code class="language-sql">COMMIT; </code></pre><pre><code>ERROR 1062 (23000): Duplicate entry 'bill' for key 'users.username' </code></pre></li><li><p>关闭该变量时，如果在事务中写入数据，执行 <code>COMMIT</code> 语句可能会返回 <code>Write conflict</code> 错误。返回该错误时，TiDB 会回滚当前事务。</p><p> 在下面这个例子中，当有并发事务写入时，跳过悲观锁导致事务提交时报出 <code>Write conflict</code> 错误并回滚。</p><pre><code class="language-sql">DROP TABLE IF EXISTS users; CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, username VARCHAR(60) NOT NULL, UNIQUE KEY (username) SET tidb_constraint_check_in_place_pessimistic = OFF; BEGIN PESSIMISTIC; INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); -- Query OK, 3 rows affected </code></pre><p> 然后另一个会话中写入了 <code>bill</code>：</p><pre><code class="language-sql">INSERT INTO users (username) VALUES ('bill'); -- Query OK, 1 row affected </code></pre><p> 在第一个会话中提交时，TiDB 会报出 <code>Write conflict</code> 错误。</p><pre><code class="language-sql">COMMIT; </code></pre><pre><code>ERROR 9007 (HY000): Write conflict, txnStartTS=435688780611190794, conflictStartTS=435688783311536129, conflictCommitTS=435688783311536130, key={tableID=74, indexID=1, indexValues={bill, }} primary={tableID=74, indexID=1, indexValues={bill, }}, reason=LazyUniquenessCheck [try again later] </code></pre></li><li><p>关闭该变量时，如果多个悲观事务之间存在写冲突，悲观锁可能会在其它悲观事务提交时被强制回滚，因此产生 <code>PessimisticLockNotFound</code> 错误。发生该错误时，说明该业务不适合推迟悲观事务的唯一约束检查，应考虑调整业务避免冲突，或在发生错误后重试事务。</p></li><li><p>关闭该变量会导致悲观事务中可能报出错误 <code>8147: LazyUniquenessCheckFailure</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-152gid5" 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-17ioyuk">注意</div><p>返回 8147 错误时当前事务回滚。</p></div></div></div><p> 下面的例子在 INSERT 语句执行时跳过了一次加锁后，在 DELETE 语句执行时对该唯一索引加锁并检查，即会在该语句报错：</p><pre><code class="language-sql">SET tidb_constraint_check_in_place_pessimistic = OFF; BEGIN PESSIMISTIC; INSERT INTO users (username) VALUES ('jane'), ('chris'), ('bill'); -- Query OK, 3 rows affected DELETE FROM users where username = 'bill'; </code></pre><pre><code>ERROR 8147 (23000): transaction aborted because lazy uniqueness check is enabled and an error occurred: [kv:1062]Duplicate entry 'bill' for key 'users.username' </code></pre></li><li><p>关闭该变量时，<code>1062 Duplicate entry</code> 报错不一定是当前执行的 SQL 语句所发生的错误。因此，在一个事务操作多个表，且这些表有同名索引时，请注意 <code>1062</code> 报错信息中提示的是哪个表的哪个索引发生了错误。</p></li></ul><h2 id="主键约束" style="position:relative"><a href="#%E4%B8%BB%E9%94%AE%E7%BA%A6%E6%9D%9F" aria-label="主键约束 permalink" class="anchor before"><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>主键约束</h2><p>与 MySQL 行为一样，主键约束包含了唯一约束，即创建了主键约束相当于拥有了唯一约束。此外，TiDB 其他的主键约束规则也与 MySQL 相似。例如：</p><pre><code class="language-sql">CREATE TABLE t1 (a INT NOT NULL PRIMARY KEY); </code></pre><pre><code>Query OK, 0 rows affected (0.12 sec) </code></pre><pre><code class="language-sql">CREATE TABLE t2 (a INT NULL PRIMARY KEY); </code></pre><pre><code>ERROR 1171 (42000): All parts of a PRIMARY KEY must be NOT NULL; if you need NULL in a key, use UNIQUE instead </code></pre><pre><code class="language-sql">CREATE TABLE t3 (a INT NOT NULL PRIMARY KEY, b INT NOT NULL PRIMARY KEY); </code></pre><pre><code>ERROR 1068 (42000): Multiple primary key defined </code></pre><pre><code class="language-sql">CREATE TABLE t4 (a INT NOT NULL, b INT NOT NULL, PRIMARY KEY (a,b)); </code></pre><pre><code>Query OK, 0 rows affected (0.10 sec) </code></pre><p>分析：</p><ul><li>表 <code>t2</code> 创建失败，因为定义为主键的列 <code>a</code> 不能允许 <code>NULL</code> 值。</li><li>表 <code>t3</code> 创建失败，因为一张表只能有一个主键。</li><li>表 <code>t4</code> 创建成功，因为虽然只能有一个主键，但 TiDB 支持定义一个多列组合作为复合主键。</li></ul><p>除上述规则外，TiDB 目前仅支持对 <code>NONCLUSTERED</code> 的主键进行添加和删除操作。例如：</p><pre><code class="language-sql">CREATE TABLE t5 (a INT NOT NULL, b INT NOT NULL, PRIMARY KEY (a,b) CLUSTERED); ALTER TABLE t5 DROP PRIMARY KEY; </code></pre><pre><code>ERROR 8200 (HY000): Unsupported drop primary key when the table is using clustered index </code></pre><pre><code class="language-sql">CREATE TABLE t5 (a INT NOT NULL, b INT NOT NULL, PRIMARY KEY (a,b) NONCLUSTERED); ALTER TABLE t5 DROP PRIMARY KEY; </code></pre><pre><code>Query OK, 0 rows affected (0.10 sec) </code></pre><p>要了解关于 <code>CLUSTERED</code> 主键的详细信息，请参考<a href="/zh/tidb/dev/clustered-indexes">聚簇索引</a>。</p><h2 id="外键约束" style="position:relative"><a href="#%E5%A4%96%E9%94%AE%E7%BA%A6%E6%9D%9F" aria-label="外键约束 permalink" class="anchor before"><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>外键约束</h2><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardInfo MuiAlert-standard css-152gid5" 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-17ioyuk">注意</div><p>TiDB 从 v6.6.0 开始支持<a href="/zh/tidb/dev/foreign-key">外键约束</a>。在 v6.6.0 之前，TiDB 支持创建和删除外键约束，但外键约束并不生效。升级到 v6.6.0 后，可以先删除不生效的外键后再创建外键使外键约束生效。</p></div></div></div><p>TiDB 支持创建外键约束。例如：</p><pre><code class="language-sql">CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, doc JSON CREATE TABLE orders ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, user_id INT NOT NULL, doc JSON, FOREIGN KEY fk_user_id (user_id) REFERENCES users(id) </code></pre><pre><code class="language-sql">SELECT table_name, column_name, constraint_name, referenced_table_name, referenced_column_name FROM information_schema.key_column_usage WHERE table_name IN ('users', 'orders'); </code></pre><pre><code>+------------+-------------+-----------------+-----------------------+------------------------+ | table_name | column_name | constraint_name | referenced_table_name | referenced_column_name | +------------+-------------+-----------------+-----------------------+------------------------+ | users | id | PRIMARY | NULL | NULL | | orders | id | PRIMARY | NULL | NULL |