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MuiInputBase-sizeSmall MuiInputBase-adornedStart css-10r6rap"><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-1a7iucg"/><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></header><div class="PingCAP-Doc MuiBox-root css-s1brf2"><div class="MuiBox-root css-hboir5"><aside class="MuiBox-root css-2tzg8"><div class="MuiBox-root css-ysaqso"><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-hg1lfe">dev</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-z7v9yr" target="_blank" href="https://docs.pingcap.com/zh" style="text-decoration:none;width:100%;color:inherit"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" id="left-nav-treeview-0-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">文档中心</div></div></div></div></div></li></a><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">关于 TiDB</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">快速上手</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-13dmm4z" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">应用开发</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/dev/dev-guide-overview"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" id="left-nav-treeview-0-3-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">概览</div></div></div></div></div></li></a><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">快速开始</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">示例程序</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">连接到 TiDB</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-4" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">数据库模式设计</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-5" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">数据写入</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">数据读取</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">事务</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">优化 SQL 性能</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-3-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-13dmm4z" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">故障诊断</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/dev/dev-guide-troubleshoot-overview"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" id="left-nav-treeview-0-3-9-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">SQL 或事务问题</div></div></div></div></div></li></a><a aria-current="page" style="text-decoration:none;width:100%;color:inherit" class="" href="/zh/tidb/dev/dev-guide-unstable-result-set"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-selected="true" id="left-nav-treeview-0-3-9-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content Mui-expanded Mui-selected" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">结果集不稳定</div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/dev-guide-timeouts-in-tidb"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" id="left-nav-treeview-0-3-9-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">超时</div></div></div></div></div></li></a></div></div></ul></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-10" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">引用文档</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">云原生开发环境</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">第三方工具支持</div></div></div></div></div></li></div></div></ul></li><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">部署标准集群</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" focusable="false" aria-hidden="true" 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MuiTypography-body1 css-1rc6ywa">参考指南</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">常见问题解答 (FAQ)</div></div></div></div></div></li><li class="MuiTreeItem-root css-14t19hb" 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-zfdk9c 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-hkir54" 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="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">版本发布历史</div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/dev/glossary"><li class="MuiTreeItem-root css-14t19hb" role="treeitem" id="left-nav-treeview-0-16" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-zfdk9c MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><div class="MuiBox-root css-3o0h5k"/><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1rc6ywa">术语表</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="结果集不稳定" style="position:relative">结果集不稳定<a href="#%E7%BB%93%E6%9E%9C%E9%9B%86%E4%B8%8D%E7%A8%B3%E5%AE%9A" aria-label="结果集不稳定 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>本章将叙述结果集不稳定错误的处理办法。</p><h2 id="group-by" style="position:relative">group by<a href="#group-by" aria-label="group by 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>出于便捷的考量，MySQL “扩展” 了 group by 语法，使 select 子句可以引用未在 group by 子句中声明的非聚集字段，也就是 non-full group by 语法。在其他数据库中，这被认为是一种语法错误，因为这会导致结果集不稳定。</p><p>在下例的 3 条 SQL 语句中，第一条 SQL 使用了 full group by 语法，所有在 select 子句中引用的字段，都在 group by 子句中有所声明，所以它的结果集是稳定的，可以看到 class 与 stuname 的全部组合共有三种；第二条与第三条是同一个 SQL，但它在两次执行时得到了不同的结果，这条 SQL 的 group by 子句中仅声明了一个 class 字段，因此结果集只会针对 class 进行聚集，class 的唯一值有两个，也就是说结果集中只会包含两行数据，而 class 与 stuname 的全部组合共有三种，班级 2018_CS_03 有两位同学，每次执行时返回哪位同学是没有语义上的限制的，都是符合语义的结果。</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> a.class, a.stuname, <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> a.class, a.stuname <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class, a.stuname; <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> class <span class="hljs-operator">|</span> stuname <span class="hljs-operator">|</span> <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> <span class="hljs-number">95.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> <span class="hljs-number">99.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> <span class="hljs-number">95.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-number">3</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) mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">select</span> a.class, a.stuname, <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> a.class <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class, a.stuname; <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> class <span class="hljs-operator">|</span> stuname <span class="hljs-operator">|</span> <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> <span class="hljs-number">95.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> <span class="hljs-number">99.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-number">2</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) mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">select</span> a.class, a.stuname, <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> a.class <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class, a.stuname; <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> class <span class="hljs-operator">|</span> stuname <span class="hljs-operator">|</span> <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> <span class="hljs-number">95.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> <span class="hljs-number">99.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-number">2</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><p>因此，想保障 group by 语句结果集的稳定，请使用 full group by 语法。</p><p>MySQL 提供了一个 SQL_MODE 开关 ONLY_FULL_GROUP_BY 来控制是否进行 full group by 语法的检查，TiDB 也兼容了这个 SQL_MODE 开关：</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> a.class, a.stuname, <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> a.class <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class, a.stuname; <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> class <span class="hljs-operator">|</span> stuname <span class="hljs-operator">|</span> <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> <span class="hljs-number">95.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> <span class="hljs-number">99.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+------------------+</span> <span class="hljs-number">2</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) mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">set</span> @<span class="hljs-variable">@sql</span>_mode<span class="hljs-operator">=</span><span class="hljs-string">'STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY'</span>; Query OK, <span class="hljs-number">0</span> <span class="hljs-keyword">rows</span> affected (<span class="hljs-number">0.01</span> sec) mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">select</span> a.class, a.stuname, <span class="hljs-built_in">max</span>(b.courscore) <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">group</span> <span class="hljs-keyword">by</span> a.class <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class, a.stuname; ERROR <span class="hljs-number">1055</span> (<span class="hljs-number">42000</span>): Expression #<span class="hljs-number">2</span> <span class="hljs-keyword">of</span> <span class="hljs-keyword">ORDER</span> <span class="hljs-keyword">BY</span> <span class="hljs-keyword">is</span> <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> clause <span class="hljs-keyword">and</span> <span class="hljs-keyword">contains</span> nonaggregated <span class="hljs-keyword">column</span> <span class="hljs-string">''</span> which <span class="hljs-keyword">is</span> <span class="hljs-keyword">not</span> functionally dependent <span class="hljs-keyword">on</span> columns <span class="hljs-keyword">in</span> <span class="hljs-keyword">GROUP</span> <span class="hljs-keyword">BY</span> clause; this <span class="hljs-keyword">is</span> incompatible <span class="hljs-keyword">with</span> sql_mode<span class="hljs-operator">=</span>only_full_group_by </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><strong>运行结果简述</strong>：上例为 sql_mode 设置了 ONLY_FULL_GROUP_BY 的效果。</p><h2 id="order-by" style="position:relative">order by<a href="#order-by" aria-label="order by 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>在 SQL 的语义中，只有使用了 order by 语法才会保障结果集的顺序输出。而单机数据库由于数据都存储在一台服务器上，在不进行数据重组时，多次执行的结果往往是稳定的，有些数据库(尤其是 MySQL InnoDB 存储引擎)还会按照主键或索引的顺序进行结果集的输出。TiDB 是分布式数据库，数据被存储在多台服务器上，另外 TiDB 层不缓存数据页，因此不含 order by 的 SQL 语句的结果集展现顺序容易被感知到不稳定。想要按顺序输出的结果集，需明确地把要排序的字段添加到 order by 子句中，这符合 SQL 的语义。</p><p>在下面的案例中，用户只在 order by 子句中添加了一个字段，TiDB 只会按照这一个字段进行排序。</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> a.class, a.stuname, b.course, b.courscore <span class="hljs-keyword">from</span> stu_info a <span class="hljs-keyword">join</span> stu_score b <span class="hljs-keyword">on</span> a.stuno<span class="hljs-operator">=</span>b.stuno <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> a.class; <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+-------------------------+-----------+</span> <span class="hljs-operator">|</span> class <span class="hljs-operator">|</span> stuname <span class="hljs-operator">|</span> course <span class="hljs-operator">|</span> courscore <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+-------------------------+-----------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> PrinciplesofDatabase <span class="hljs-operator">|</span> <span class="hljs-number">60.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> English <span class="hljs-operator">|</span> <span class="hljs-number">43.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> OpSwimming <span class="hljs-operator">|</span> <span class="hljs-number">67.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> OpFencing <span class="hljs-operator">|</span> <span class="hljs-number">76.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> FundamentalsofCompiling <span class="hljs-operator">|</span> <span class="hljs-number">88.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> OperatingSystem <span class="hljs-operator">|</span> <span class="hljs-number">90.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> PrincipleofStatistics <span class="hljs-operator">|</span> <span class="hljs-number">69.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> ProbabilityTheory <span class="hljs-operator">|</span> <span class="hljs-number">76.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> Physics <span class="hljs-operator">|</span> <span class="hljs-number">63.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> AdvancedMathematics <span class="hljs-operator">|</span> <span class="hljs-number">95.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> LinearAlgebra <span class="hljs-operator">|</span> <span class="hljs-number">92.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_01 <span class="hljs-operator">|</span> MonkeyDLuffy <span class="hljs-operator">|</span> DiscreteMathematics <span class="hljs-operator">|</span> <span class="hljs-number">89.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> PrinciplesofDatabase <span class="hljs-operator">|</span> <span class="hljs-number">88.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> English <span class="hljs-operator">|</span> <span class="hljs-number">79.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> OpBasketball <span class="hljs-operator">|</span> <span class="hljs-number">92.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> OpTennis <span class="hljs-operator">|</span> <span class="hljs-number">94.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> LinearAlgebra <span class="hljs-operator">|</span> <span class="hljs-number">6.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> AdvancedMathematics <span class="hljs-operator">|</span> <span class="hljs-number">5.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> DiscreteMathematics <span class="hljs-operator">|</span> <span class="hljs-number">72.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> ProbabilityTheory <span class="hljs-operator">|</span> <span class="hljs-number">12.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> PrincipleofStatistics <span class="hljs-operator">|</span> <span class="hljs-number">20.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> OperatingSystem <span class="hljs-operator">|</span> <span class="hljs-number">36.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> FundamentalsofCompiling <span class="hljs-operator">|</span> <span class="hljs-number">2.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> DiscreteMathematics <span class="hljs-operator">|</span> <span class="hljs-number">14.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> PrinciplesofDatabase <span class="hljs-operator">|</span> <span class="hljs-number">9.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> English <span class="hljs-operator">|</span> <span class="hljs-number">60.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> OpTableTennis <span class="hljs-operator">|</span> <span class="hljs-number">12.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> OpPiano <span class="hljs-operator">|</span> <span class="hljs-number">99.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> FundamentalsofCompiling <span class="hljs-operator">|</span> <span class="hljs-number">43.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> OperatingSystem <span class="hljs-operator">|</span> <span class="hljs-number">95.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> PrincipleofStatistics <span class="hljs-operator">|</span> <span class="hljs-number">90.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> ProbabilityTheory <span class="hljs-operator">|</span> <span class="hljs-number">87.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> Physics <span class="hljs-operator">|</span> <span class="hljs-number">65.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> AdvancedMathematics <span class="hljs-operator">|</span> <span class="hljs-number">55.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> SpongeBob <span class="hljs-operator">|</span> LinearAlgebra <span class="hljs-operator">|</span> <span class="hljs-number">60.5</span> <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">2018</span>_CS_03 <span class="hljs-operator">|</span> PatrickStar <span class="hljs-operator">|</span> Physics <span class="hljs-operator">|</span> <span class="hljs-number">6.0</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">------------+--------------+-------------------------+-----------+</span> <span class="hljs-number">36</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><p>当遇到相同的 order by 值时，排序结果不稳定。为减少随机性，应当尽可能保持 order by 值的唯一性。不能保证唯一的继续加，保证 order by 的字段组合是唯一时，结果才能唯一。</p><h2 id="由于-group_concat-中没有使用-order-by-导致结果集不稳定" style="position:relative">由于 group_concat() 中没有使用 order by 导致结果集不稳定<a href="#%E7%94%B1%E4%BA%8E-group_concat-%E4%B8%AD%E6%B2%A1%E6%9C%89%E4%BD%BF%E7%94%A8-order-by-%E5%AF%BC%E8%87%B4%E7%BB%93%E6%9E%9C%E9%9B%86%E4%B8%8D%E7%A8%B3%E5%AE%9A" aria-label="由于 group_concat 中没有使用 order by 导致结果集不稳定 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>结果集不稳定是因为 TiDB 是并行地从存储层读取数据，所以 <code>group_concat()</code> 在不加 order by 的情况下得到的结果集展现顺序容易被感知到不稳定。</p><p><code>group_concat()</code> 要获取到按顺序输出的结果集，需要把用于排序的字段添加到 order by 子句中，这样才符合 SQL 的语义。在下面的案例中，使用 <code>group_concat()</code> 不加 order by 的情况下拼接 customer_id，造成结果集不稳定：</p><ol><li><p>不加 order by</p><p>第一次查询：</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> GROUP_CONCAT( customer_id SEPARATOR <span class="hljs-string">','</span> ) <span class="hljs-keyword">FROM</span> customer <span class="hljs-keyword">where</span> customer_id <span class="hljs-keyword">like</span> <span class="hljs-string">'200002%'</span>; <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> GROUP_CONCAT(customer_id SEPARATOR <span class="hljs-string">','</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">20000200992</span>,<span class="hljs-number">20000200993</span>,<span class="hljs-number">20000200994</span>,<span class="hljs-number">20000200995</span>,<span class="hljs-number">20000200996</span>,<span class="hljs-number">20000200.</span>.. <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>第二次查询：</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> GROUP_CONCAT( customer_id SEPARATOR <span class="hljs-string">','</span> ) <span class="hljs-keyword">FROM</span> customer <span class="hljs-keyword">where</span> customer_id <span class="hljs-keyword">like</span> <span class="hljs-string">'200002%'</span>; <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> GROUP_CONCAT(customer_id SEPARATOR <span class="hljs-string">','</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">20000203040</span>,<span class="hljs-number">20000203041</span>,<span class="hljs-number">20000203042</span>,<span class="hljs-number">20000203043</span>,<span class="hljs-number">20000203044</span>,<span class="hljs-number">20000203.</span>.. <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></li><li><p>加 order by</p><p>第一次查询：</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> GROUP_CONCAT( customer_id <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> customer_id SEPARATOR <span class="hljs-string">','</span> ) <span class="hljs-keyword">FROM</span> customer <span class="hljs-keyword">where</span> customer_id <span class="hljs-keyword">like</span> <span class="hljs-string">'200002%'</span>; <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> GROUP_CONCAT(customer_id SEPARATOR <span class="hljs-string">','</span>) <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-------------------------------------------------------------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-number">20000200000</span>,<span class="hljs-number">20000200001</span>,<span class="hljs-number">20000200002</span>,<span class="hljs-number">20000200003</span>,<span class="hljs-number">20000200004</span>,<span class="hljs-number">20000200.</span>.. <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>第二次查询：</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> GROUP_CONCAT( customer_id <span class="hljs-keyword">order</span> <span class="hljs-keyword">by</span> customer_id SEPARATOR <span class="hljs-string">','</span> ) <span class="hljs-keyword">FROM</span> customer <span class="hljs-keyword">where</span> customer_id <span class="hljs-keyword">like</span> <span class="hljs-string">'200002%'</span>;