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css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">部署标准集群</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-5" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">数据迁移</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-6" tabindex="-1" 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css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">监控与告警</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-9" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">故障诊断</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-10" tabindex="-1" 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class="MuiTypography-root MuiTypography-body1 css-1g11p7i">TiDB 工具</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-13" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">参考指南</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div 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style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">存储引擎 TiKV</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">存储引擎 TiFlash</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">TiDB 分布式执行框架</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/system-variables/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-4" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">系统变量</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/system-variable-reference/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-5" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">系统变量索引</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/status-variables/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-6" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">服务器状态变量</div></div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-7" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">配置文件参数</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-8" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">CLI</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-9" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">命令行参数</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-10" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">监控指标</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-11" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">权限</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-13-12" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-2jyri7"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-0-13-12-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-11fv84e" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 语言结构和语法</div></div></div></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-0-0" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">属性</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/literal-values/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-0-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">字面值</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/schema-object-names/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-0-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">Schema 对象名</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/keywords/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-0-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">关键字</div></div></div></div></div></div></li></a><a aria-current="page" style="text-decoration:none;width:100%;color:inherit" class="" href="/zh/tidb/stable/user-defined-variables/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-selected="true" id="left-nav-treeview-0-0-13-12-0-4" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content Mui-expanded Mui-selected" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">用户自定义变量</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/expression-syntax/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-0-5" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">表达式语法</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/comment-syntax/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-0-6" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-gwjyeh"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">注释语法</div></div></div></div></div></div></li></a></div></div></ul></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-1" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 语句</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-2" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">数据类型</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-3" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">函数与操作符</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/clustered-indexes/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-4" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">聚簇索引</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/vector-search-index/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-5" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">向量索引</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/constraints/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-6" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">约束</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/generated-columns/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-7" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">生成列</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/sql-mode/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-8" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">SQL 模式</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/table-attributes/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-9" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">表属性</div></div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-10" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">事务</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/views/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-11" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">视图</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/partitioned-table/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-12" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">分区表</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/temporary-tables/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-13" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">临时表</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/cached-tables/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-14" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">缓存表</div></div></div></div></div></div></li></a><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/foreign-key/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-15" tabindex="-1" 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class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">字符集和排序规则</div></div></div></div></div></div></li><a style="text-decoration:none;width:100%;color:inherit" href="/zh/tidb/stable/placement-rules-in-sql/"><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" id="left-nav-treeview-0-0-13-12-17" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-xeut16"><div class="MuiBox-root css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">Placement Rules in SQL</div></div></div></div></div></div></li></a><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-13-12-18" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div 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格式</div></div></div></div></div></div></li></a></div></div></ul></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-14" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div class="css-fhn3dm MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-w8t2sr"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-1guu2k2" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">常见问题解答 (FAQ)</div></div></div></div></div></div></li><li class="MuiTreeItem-root css-1p2jk91" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-0-15" tabindex="-1" style="margin-top:4px;margin-bottom:4px"><div 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css-f81823"/><div class="css-szjynw"><div class="MuiBox-root css-1uoa4hf"><div class="MuiTypography-root MuiTypography-body1 css-1g11p7i">术语表</div></div></div></div></div></div></li></a></ul></div></aside><main class="MuiBox-root css-sb2sd0"><div class="MuiBox-root css-w0vdto"><div class="css-1q5cbag"><div class="MuiBox-root css-was4pq"><div class="MuiContainer-root MuiContainer-maxWidthLg MuiContainer-disableGutters doc-content css-5csqms"><div class="markdown-body MuiBox-root css-0"><h1 id="用户自定义变量" style="position:relative">用户自定义变量<a href="#%E7%94%A8%E6%88%B7%E8%87%AA%E5%AE%9A%E4%B9%89%E5%8F%98%E9%87%8F" aria-label="用户自定义变量 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><div class="MuiBox-root css-1weqspv"><div class="MuiPaper-root MuiPaper-elevation MuiPaper-rounded MuiPaper-elevation0 MuiAlert-root MuiAlert-standardError MuiAlert-standard css-kdwypz" role="alert"><div class="MuiAlert-icon css-1l54tgj"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ErrorOutlineIcon"><path d="M11 15h2v2h-2zm0-8h2v6h-2zm.99-5C6.47 2 2 6.48 2 12s4.47 10 9.99 10C17.52 22 22 17.52 22 12S17.52 2 11.99 2zM12 20c-4.42 0-8-3.58-8-8s3.58-8 8-8 8 3.58 8 8-3.58 8-8 8z"/></svg></div><div class="MuiAlert-message css-1xsto0d"><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-m00e13">警告</div><p>当前该功能为实验特性，不建议在生产环境中使用。</p></div></div></div><p>本文介绍 TiDB 的用户自定义变量的概念，以及设置和读取用户自定义变量的方法。</p><p>用户自定义变量格式为 <code>@var_name</code>。组成 <code>var_name</code> 的字符可以是任何能够组成标识符 (identifier) 的字符，包括数字 <code>0-9</code>、字母 <code>a-zA-Z</code>、下划线 <code>_</code>、美元符号 <code>$</code> 以及 UTF-8 字符。此外，还包括英文句号 <code>.</code>。用户自定义变量是大小写不敏感的。</p><p>用户自定义变量跟 session 绑定，当前设置的用户变量只在当前连接中可见，其他客户端连接无法查看。</p><h2 id="设置用户自定义变量" style="position:relative">设置用户自定义变量<a href="#%E8%AE%BE%E7%BD%AE%E7%94%A8%E6%88%B7%E8%87%AA%E5%AE%9A%E4%B9%89%E5%8F%98%E9%87%8F" aria-label="设置用户自定义变量 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>用 <a href="/zh/tidb/stable/sql-statement-set-variable/"><code>SET</code> 语句</a>可以设置用户自定义变量，语法为 <code>SET @var_name = expr [, @var_name = expr] ...;</code>。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@favorite</span>_db <span class="hljs-operator">=</span> <span class="hljs-string">'TiDB'</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@a</span> <span class="hljs-operator">=</span> <span class="hljs-string">'a'</span>, <span class="hljs-variable">@b</span> <span class="hljs-operator">=</span> <span class="hljs-string">'b'</span>, <span class="hljs-variable">@c</span> <span class="hljs-operator">=</span> <span class="hljs-string">'c'</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>其中赋值符号还可以使用 <code>:=</code>。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@favorite</span>_db :<span class="hljs-operator">=</span> <span class="hljs-string">'TiDB'</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>赋值符号右边的内容可以是任意合法的表达式。例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@c</span> <span class="hljs-operator">=</span> <span class="hljs-variable">@a</span> <span class="hljs-operator">+</span> <span class="hljs-variable">@b</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@c</span> <span class="hljs-operator">=</span> b<span class="hljs-string">'1000001'</span> <span class="hljs-operator">+</span> b<span class="hljs-string">'1000001'</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><h2 id="读取用户自定义变量" style="position:relative">读取用户自定义变量<a href="#%E8%AF%BB%E5%8F%96%E7%94%A8%E6%88%B7%E8%87%AA%E5%AE%9A%E4%B9%89%E5%8F%98%E9%87%8F" aria-label="读取用户自定义变量 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>要读取一个用户自定义变量，可以使用 <code>SELECT</code> 语句查询：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-variable">@a1</span>, <span class="hljs-variable">@a2</span>, <span class="hljs-variable">@a3</span> </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+------+------+------+ | @a1 | @a2 | @a3 | +------+------+------+ | 1 | 2 | 4 | +------+------+------+ </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>还可以在 <code>SELECT</code> 语句中赋值：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-variable">@a1</span>, <span class="hljs-variable">@a2</span>, <span class="hljs-variable">@a3</span>, <span class="hljs-variable">@a4</span> :<span class="hljs-operator">=</span> <span class="hljs-variable">@a1</span><span class="hljs-operator">+</span><span class="hljs-variable">@a2</span><span class="hljs-operator">+</span><span class="hljs-variable">@a3</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+------+------+------+--------------------+ | @a1 | @a2 | @a3 | @a4 := @a1+@a2+@a3 | +------+------+------+--------------------+ | 1 | 2 | 4 | 7 | +------+------+------+--------------------+ </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>其中变量 <code>@a4</code> 在被修改或关闭连接之前，值始终为 <code>7</code>。</p><p>如果设置用户变量时用了十六进制字面量或者二进制字面量，TiDB 会把它当成二进制字符串。如果要将其设置成数字，那么可以手动加上 <code>CAST</code> 转换，或者在表达式中使用数字的运算符：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@v1</span> <span class="hljs-operator">=</span> b<span class="hljs-string">'1000001'</span>; <span class="hljs-keyword">SET</span> <span class="hljs-variable">@v2</span> <span class="hljs-operator">=</span> b<span class="hljs-string">'1000001'</span><span class="hljs-operator">+</span><span class="hljs-number">0</span>; <span class="hljs-keyword">SET</span> <span class="hljs-variable">@v3</span> <span class="hljs-operator">=</span> <span class="hljs-built_in">CAST</span>(b<span class="hljs-string">'1000001'</span> <span class="hljs-keyword">AS</span> UNSIGNED); </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-variable">@v1</span>, <span class="hljs-variable">@v2</span>, <span class="hljs-variable">@v3</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+------+------+------+ | @v1 | @v2 | @v3 | +------+------+------+ | A | 65 | 65 | +------+------+------+ </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>如果获取一个没有设置过的变量，会返回一个 NULL：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-variable">@not</span>_exist; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+------------+ | @not_exist | +------------+ | NULL | +------------+ </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><p>除了 <code>SELECT</code> 读取用户自定义变量以外，常见的用法还有 <code>PREPARE</code> 语句，例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@s</span> <span class="hljs-operator">=</span> <span class="hljs-string">'SELECT SQRT(POW(?,2) + POW(?,2)) AS hypotenuse'</span>; <span class="hljs-keyword">PREPARE</span> stmt <span class="hljs-keyword">FROM</span> <span class="hljs-variable">@s</span>; <span class="hljs-keyword">SET</span> <span class="hljs-variable">@a</span> <span class="hljs-operator">=</span> <span class="hljs-number">6</span>; <span class="hljs-keyword">SET</span> <span class="hljs-variable">@b</span> <span class="hljs-operator">=</span> <span class="hljs-number">8</span>; <span class="hljs-keyword">EXECUTE</span> stmt <span class="hljs-keyword">USING</span> <span class="hljs-variable">@a</span>, <span class="hljs-variable">@b</span>; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+------------+ | hypotenuse | +------------+ | 10 | +------------+ </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>用户自定义变量的内容不会在 SQL 语句中被当成标识符，例如：</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> t; </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-plaintext"><div class="MuiBox-root css-1qhimia">+---+ | a | +---+ | 1 | +---+ </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">SET</span> <span class="hljs-variable">@col</span> <span class="hljs-operator">=</span> "`a`"; <span class="hljs-keyword">SELECT</span> <span class="hljs-variable">@col</span> <span class="hljs-keyword">FROM</span> t;