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style="margin-top:0.1875rem;margin-bottom:0.1875rem"><style data-emotion="css khel7y">.css-khel7y{padding:0 8px;width:100%;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;cursor:pointer;-webkit-tap-highlight-color:transparent;}.css-khel7y:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-khel7y:hover{background-color:transparent;}}.css-khel7y.Mui-disabled{opacity:0.38;background-color:transparent;}.css-khel7y.Mui-focused{background-color:rgba(0, 0, 0, 0.12);}.css-khel7y.Mui-selected{background-color:rgba(25, 118, 210, 0.08);}.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.12);}@media (hover: none){.css-khel7y.Mui-selected:hover{background-color:rgba(25, 118, 210, 0.08);}}.css-khel7y.Mui-selected.Mui-focused{background-color:rgba(25, 118, 210, 0.2);}.css-khel7y .MuiTreeItem-iconContainer{margin-right:4px;width:15px;display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;}.css-khel7y .MuiTreeItem-iconContainer svg{font-size:18px;}.css-khel7y .MuiTreeItem-label{width:100%;min-width:0;padding-left:4px;position:relative;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;}</style><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css 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Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;color:inherit;font-size:0.875rem;line-height:1.25rem;}</style><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Docs Home</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">About TiDB</div></div><style data-emotion="css xjq79n">.css-xjq79n{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 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css-1hwyipb">Quick Start</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Develop</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 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style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Migrate</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Integrate</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Maintain</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Monitor and Alert</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Troubleshoot</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-10" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Performance Tuning</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Tutorials</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">TiDB Tools</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-13" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Reference</div></div><style data-emotion="css 171pefp">.css-171pefp{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:1.5rem;fill:#999999;height:1rem;width:1rem;margin-left:auto;-webkit-transform:rotate(90deg);-moz-transform:rotate(90deg);-ms-transform:rotate(90deg);transform:rotate(90deg);}</style><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-171pefp" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div><style data-emotion="css 1xxsnna">.css-1xxsnna{height:auto;overflow:visible;-webkit-transition:height 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:height 300ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;margin:0;padding:0;margin-left:17px;}</style><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css kb2j4b">.css-kb2j4b{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;min-height:1.75rem;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;padding-left:0.5rem;padding-top:0.25rem;padding-bottom:0.25rem;}</style><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Cluster Architecture</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Storage Engine - TiKV</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Storage Engine - TiFlash</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">TiDB Distributed eXecution Framework (DXF)</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-4" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/system-variables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">System Variables</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-5" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/status-variables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Server Status Variables</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Configuration File Parameters</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">CLI</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Command Line Flags</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-9" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Key Monitoring Metrics</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-10" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Security</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-11" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Privileges</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="true" id="left-nav-treeview-0-13-12" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-kb2j4b"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-171pefp" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div><ul class="MuiCollapse-root MuiCollapse-vertical MuiTreeItem-group MuiCollapse-entered css-1xxsnna" style="min-height:0px" role="group"><div class="MuiCollapse-wrapper MuiCollapse-vertical css-hboir5"><div class="MuiCollapse-wrapperInner MuiCollapse-vertical css-8atqhb"><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-12-0" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><style data-emotion="css snygwd">.css-snygwd{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;min-height:1.75rem;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;padding-left:1rem;padding-top:0.25rem;padding-bottom:0.25rem;}</style><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL Language Structure and Syntax</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-12-1" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL Statements</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-12-2" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Data Types</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-12-3" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Functions and Operators</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 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href="/tidb/stable/constraints"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Constraints</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12-6" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/generated-columns"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Generated Columns</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12-7" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/sql-mode"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">SQL Mode</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12-8" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/table-attributes"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Table Attributes</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" 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style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/temporary-tables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Temporary Tables</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12-13" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/cached-tables"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Cached Tables</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-13-12-14" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content Mui-expanded" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><a aria-current="page" style="text-decoration:none;width:100%;color:inherit" class="" href="/tidb/stable/foreign-key"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">FOREIGN KEY Constraints</div></div></a></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" aria-expanded="false" id="left-nav-treeview-0-13-12-15" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-snygwd"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 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css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Release Notes</div></div><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeMedium MuiTreeItem-ChevronRightIcon css-xjq79n" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ChevronRightIcon"><path d="M10 6 8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"/></svg></div></div></div></li><li class="MuiTreeItem-root css-1oy5rnm" role="treeitem" id="left-nav-treeview-0-16" tabindex="-1" style="margin-top:0.1875rem;margin-bottom:0.1875rem"><div class="css-khel7y MuiTreeItem-content" style="width:inherit"><div class="MuiTreeItem-iconContainer"/><div class="MuiTreeItem-label"><div class="css-znl8a3"><a style="text-decoration:none;width:100%;color:inherit" href="/tidb/stable/glossary"><div class="MuiBox-root css-8atqhb"><div class="MuiTypography-root MuiTypography-body1 css-1hwyipb">Glossary</div></div></a></div></div></div></li></ul></div></aside><style data-emotion="css sb2sd0">.css-sb2sd0{width:100%;}@media (min-width:1200px){.css-sb2sd0{max-width:calc(100% - 18.75rem);}}</style><main class="MuiBox-root css-sb2sd0"><style data-emotion="css 1rnnmjb">.css-1rnnmjb{max-width:1340px;width:100%;margin-left:auto;margin-right:auto;display:block;box-sizing:border-box;}</style><div class="MuiBox-root css-1rnnmjb"><style data-emotion="css 90fn5w">.css-90fn5w{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-flex-direction:column;-ms-flex-direction:column;flex-direction:column;}@media (min-width:0px){.css-90fn5w{-webkit-flex-direction:column-reverse;-ms-flex-direction:column-reverse;flex-direction:column-reverse;}}@media (min-width:600px){.css-90fn5w{-webkit-flex-direction:row;-ms-flex-direction:row;flex-direction:row;}}</style><div class="css-90fn5w"><style data-emotion="css vofosd">.css-vofosd{padding:1.5rem 0;}@media (min-width:0px){.css-vofosd{width:100%;}}@media (min-width:600px){.css-vofosd{width:calc(100% - 17.5rem);}}</style><div class="MuiBox-root css-vofosd"><style data-emotion="css 1ekb41w">.css-1ekb41w{width:100%;margin-left:auto;box-sizing:border-box;margin-right:auto;display:block;padding-left:16px;padding-right:16px;}@media (min-width:600px){.css-1ekb41w{padding-left:24px;padding-right:24px;}}@media (min-width:1536px){.css-1ekb41w{max-width:1536px;}}</style><div class="MuiContainer-root MuiContainer-maxWidthXl doc-content css-1ekb41w"><div class="markdown-body MuiBox-root css-0"><h1 id="foreign-key-constraints" style="position:relative"><a href="#foreign-key-constraints" aria-label="foreign key constraints permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>FOREIGN KEY Constraints</h1><p>Starting from v6.6.0, TiDB supports the foreign key feature, which allows cross-table referencing of related data, and foreign key constraints to maintain data consistency.</p><style data-emotion="css 1weqspv">.css-1weqspv{padding-top:0.5rem;padding-bottom:0.5rem;}.css-1weqspv .MuiAlert-message p{margin-bottom:0px;margin-top:0px;}</style><div class="MuiBox-root css-1weqspv"><style data-emotion="css 1rl2db2">.css-1rl2db2{font-size:0.875rem;line-height:1.25rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:rgb(95, 33, 32);background-color:rgb(253, 237, 237);display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;padding:6px 16px;}.css-1rl2db2 .MuiAlert-icon{color:#ef5350;}</style><style data-emotion="css 21rxh6">.css-21rxh6{background-color:#fff;color:rgba(0, 0, 0, 0.87);-webkit-transition:box-shadow 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1cw4hi4">.css-1cw4hi4{-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;width:1em;height:1em;display:inline-block;fill:currentColor;-webkit-flex-shrink:0;-ms-flex-negative:0;flex-shrink:0;-webkit-transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:fill 200ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;font-size:inherit;}</style><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="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><style data-emotion="css 1xsto0d">.css-1xsto0d{padding:8px 0;min-width:0;overflow:auto;}</style><div class="MuiAlert-message css-1xsto0d"><style data-emotion="css 1h2y6o4">.css-1h2y6o4{font-weight:500;margin-top:-2px;}</style><style data-emotion="css 17ioyuk">.css-17ioyuk{margin:0;font-size:1rem;line-height:1.5rem;font-family:"Helvetica Neue","sans-serif";font-weight:400;font-style:normal;color:#666666;margin-bottom:0.35em;font-weight:500;margin-top:-2px;}</style><div class="MuiTypography-root MuiTypography-body1 MuiTypography-gutterBottom MuiAlertTitle-root css-17ioyuk">Warning</div><ul><li>Currently, the foreign key feature is experimental. It is not recommended that you use it in production environments. This feature might be changed or removed without prior notice. If you find a bug, you can report an <a href="https://github.com/pingcap/tidb/issues" target="_blank" referrerpolicy="no-referrer-when-downgrade">issue</a> on GitHub.</li><li>The foreign key feature is typically employed to enforce <a href="https://en.wikipedia.org/wiki/Referential_integrity" target="_blank" referrerpolicy="no-referrer-when-downgrade">referential integrity</a> constraint checks. It might cause performance degradation, so it is recommended to conduct thorough testing before using it in performance-sensitive scenarios.</li></ul></div></div></div><p>The foreign key is defined in the child table. The syntax is as follows:</p><div class="syntax-diagram-module--root--vJoVV"><div class="syntax-diagram-module--toolbar--0ABqv buttons are-small are-light has-addons is-right"><button class="button is-light"><span class="icon"><svg stroke="currentColor" fill="currentColor" stroke-width="0" viewbox="0 0 24 24" height="1em" width="1em" xmlns="http://www.w3.org/2000/svg"><path fill="none" d="M0 0h24v24H0z"/><path d="M22 11V3h-7v3H9V3H2v8h7V8h2v10h4v3h7v-8h-7v3h-2V8h2v3h7zM7 9H4V5h3v4zm10 6h3v4h-3v-4zm0-10h3v4h-3V5z"/></svg></span><span>Diagram</span></button><button class="button is-light"><span class="icon"><svg stroke="currentColor" fill="currentColor" stroke-width="0" viewbox="0 0 24 24" height="1em" width="1em" xmlns="http://www.w3.org/2000/svg"><path fill="none" d="M0 0h24v24H0V0z"/><path d="M9.4 16.6L4.8 12l4.6-4.6L8 6l-6 6 6 6 1.4-1.4zm5.2 0l4.6-4.6-4.6-4.6L16 6l6 6-6 6-1.4-1.4z"/></svg></span><span>Source</span></button></div><div class="syntax-diagram-module--container--eSGQz"><dl><dt>ForeignKeyDef</dt><dd><svg class="railroad-diagram" width="1955" height="65" viewbox="0 0 1955 65"><g transform="translate(.5 .5)"><g><path d="M2 18v8l8-4Zm8 0v8l8-4Zm8 4h4" class="start-end"/></g><path d="M22 22h10"/><g><path d="M32 22h0"/><path d="M1923 22h0"/><g><path d="M32 22h0"/><path d="M283 22h0"/><path d="M32 22a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10"/><g><path d="M52 2h211"/></g><path d="M263 2a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10"/><path d="M32 22h20"/><g><path d="M52 22h0"/><path d="M263 22h0"/><g class="terminal"><path d="M52 22h0"/><path d="M168 22h0"/><rect x="52" y="11" width="116" height="22" rx="10" ry="10"/><text x="110" y="26">CONSTRAINT</text></g><path d="M168 22h10"/><path d="M178 22h10"/><g class="non-terminal"><path d="M188 22h0"/><path d="M263 22h0"/><rect x="188" y="11" width="75" height="22"/><text x="225.5" y="26">Identifier</text></g></g><path d="M263 22h20"/></g><path d="M283 22h10"/><g class="terminal"><path d="M293 22h0"/><path d="M380 22h0"/><rect x="293" y="11" width="87" height="22" rx="10" ry="10"/><text x="336.5" y="26">FOREIGN</text></g><path d="M380 22h10"/><path d="M390 22h10"/><g class="terminal"><path d="M400 22h0"/><path d="M448 22h0"/><rect x="400" y="11" width="48" height="22" rx="10" ry="10"/><text x="424" y="26">KEY</text></g><path d="M448 22h10"/><g><path d="M458 22h0"/><path d="M573 22h0"/><path d="M458 22a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10"/><g><path d="M478 2h75"/></g><path d="M553 2a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10"/><path d="M458 22h20"/><g class="non-terminal"><path d="M478 22h0"/><path d="M553 22h0"/><rect x="478" y="11" width="75" height="22"/><text x="515.5" y="26">Identifier</text></g><path d="M553 22h20"/></g><path d="M573 22h10"/><g class="terminal"><path d="M583 22h0"/><path d="M610 22h0"/><rect x="583" y="11" width="27" height="22" rx="10" ry="10"/><text x="596.5" y="26">(</text></g><path d="M610 22h10"/><path d="M620 22h10"/><g><path d="M630 22h0"/><path d="M751 22h0"/><path d="M630 22h10"/><g class="non-terminal"><path d="M640 22h0"/><path d="M741 22h0"/><rect x="640" y="11" width="101" height="22"/><text x="690.5" y="26">ColumnName</text></g><path d="M741 22h10"/><path d="M640 22a10 10 0 0 0 -10 10v10a10 10 0 0 0 10 10"/><g class="terminal"><path d="M640 52h0"/><path d="M665 52h76"/><rect x="640" y="41" width="25" height="22" rx="10" ry="10"/><text x="652.5" y="56">,</text></g><path d="M741 52a10 10 0 0 0 10 -10v-10a10 10 0 0 0 -10 -10"/></g><path d="M751 22h10"/><path d="M761 22h10"/><g class="terminal"><path d="M771 22h0"/><path d="M798 22h0"/><rect x="771" y="11" width="27" height="22" rx="10" ry="10"/><text x="784.5" y="26">)</text></g><path d="M798 22h10"/><path d="M808 22h10"/><g class="terminal"><path d="M818 22h0"/><path d="M933 22h0"/><rect x="818" y="11" width="115" height="22" rx="10" ry="10"/><text x="875.5" y="26">REFERENCES</text></g><path d="M933 22h10"/><path d="M943 22h10"/><g class="non-terminal"><path d="M953 22h0"/><path d="M1041 22h0"/><rect x="953" y="11" width="88" height="22"/><text x="997" y="26">TableName</text></g><path d="M1041 22h10"/><path d="M1051 22h10"/><g class="terminal"><path d="M1061 22h0"/><path d="M1088 22h0"/><rect x="1061" y="11" width="27" height="22" rx="10" ry="10"/><text x="1074.5" y="26">(</text></g><path d="M1088 22h10"/><path d="M1098 22h10"/><g><path d="M1108 22h0"/><path d="M1229 22h0"/><path d="M1108 22h10"/><g class="non-terminal"><path d="M1118 22h0"/><path d="M1219 22h0"/><rect x="1118" y="11" width="101" height="22"/><text x="1168.5" y="26">ColumnName</text></g><path d="M1219 22h10"/><path d="M1118 22a10 10 0 0 0 -10 10v10a10 10 0 0 0 10 10"/><g class="terminal"><path d="M1118 52h0"/><path d="M1143 52h76"/><rect x="1118" y="41" width="25" height="22" rx="10" ry="10"/><text x="1130.5" y="56">,</text></g><path d="M1219 52a10 10 0 0 0 10 -10v-10a10 10 0 0 0 -10 -10"/></g><path d="M1229 22h10"/><path d="M1239 22h10"/><g class="terminal"><path d="M1249 22h0"/><path d="M1276 22h0"/><rect x="1249" y="11" width="27" height="22" rx="10" ry="10"/><text x="1262.5" y="26">)</text></g><path d="M1276 22h10"/><g><path d="M1286 22h0"/><path d="M1603 22h0"/><path d="M1286 22a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10"/><g><path d="M1306 2h277"/></g><path d="M1583 2a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10"/><path d="M1286 22h20"/><g><path d="M1306 22h0"/><path d="M1583 22h0"/><g class="terminal"><path d="M1306 22h0"/><path d="M1348 22h0"/><rect x="1306" y="11" width="42" height="22" rx="10" ry="10"/><text x="1327" y="26">ON</text></g><path d="M1348 22h10"/><path d="M1358 22h10"/><g class="terminal"><path d="M1368 22h0"/><path d="M1443 22h0"/><rect x="1368" y="11" width="75" height="22" rx="10" ry="10"/><text x="1405.5" y="26">DELETE</text></g><path d="M1443 22h10"/><path d="M1453 22h10"/><g class="non-terminal"><path d="M1463 22h0"/><path d="M1583 22h0"/><rect x="1463" y="11" width="120" height="22"/><text x="1523" y="26">ReferenceOption</text></g></g><path d="M1583 22h20"/></g><g><path d="M1603 22h0"/><path d="M1923 22h0"/><path d="M1603 22a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10"/><g><path d="M1623 2h280"/></g><path d="M1903 2a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10"/><path d="M1603 22h20"/><g><path d="M1623 22h0"/><path d="M1903 22h0"/><g class="terminal"><path d="M1623 22h0"/><path d="M1665 22h0"/><rect x="1623" y="11" width="42" height="22" rx="10" ry="10"/><text x="1644" y="26">ON</text></g><path d="M1665 22h10"/><path d="M1675 22h10"/><g class="terminal"><path d="M1685 22h0"/><path d="M1763 22h0"/><rect x="1685" y="11" width="78" height="22" rx="10" ry="10"/><text x="1724" y="26">UPDATE</text></g><path d="M1763 22h10"/><path d="M1773 22h10"/><g class="non-terminal"><path d="M1783 22h0"/><path d="M1903 22h0"/><rect x="1783" y="11" width="120" height="22"/><text x="1843" y="26">ReferenceOption</text></g></g><path d="M1903 22h20"/></g></g><path d="M1923 22h10"/><path d="M1933 22h4m0-4v8l16-8v8Z" class="start-end"/></g></svg></dd><dt>ReferenceOption</dt><dd><svg class="railroad-diagram" width="238" height="146" viewbox="0 0 238 146"><g transform="translate(.5 .5)"><g><path d="M2 9v8l8-4Zm8 0v8l8-4Zm8 4h4" class="start-end"/></g><g><path d="M22 13h0"/><path d="M216 13h0"/><path d="M22 13h20"/><g class="terminal"><path d="M42 13h0"/><path d="M135 13h61"/><rect x="42" y="2" width="93" height="22" rx="10" ry="10"/><text x="88.5" y="17">RESTRICT</text></g><path d="M196 13h20"/><path d="M22 13a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10"/><g class="terminal"><path d="M42 43h0"/><path d="M132 43h64"/><rect x="42" y="32" width="90" height="22" rx="10" ry="10"/><text x="87" y="47">CASCADE</text></g><path d="M196 43a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10"/><path d="M22 13a10 10 0 0 1 10 10v40a10 10 0 0 0 10 10"/><g><path d="M42 73h0"/><path d="M167 73h29"/><g class="terminal"><path d="M42 73h0"/><path d="M90 73h0"/><rect x="42" y="62" width="48" height="22" rx="10" ry="10"/><text x="66" y="77">SET</text></g><path d="M90 73h10"/><path d="M100 73h10"/><g class="terminal"><path d="M110 73h0"/><path d="M167 73h0"/><rect x="110" y="62" width="57" height="22" rx="10" ry="10"/><text x="138.5" y="77">NULL</text></g></g><path d="M196 73a10 10 0 0 0 10 -10v-40a10 10 0 0 1 10 -10"/><path d="M22 13a10 10 0 0 1 10 10v70a10 10 0 0 0 10 10"/><g><path d="M42 103h0"/><path d="M196 103h0"/><g class="terminal"><path d="M42 103h0"/><path d="M90 103h0"/><rect x="42" y="92" width="48" height="22" rx="10" ry="10"/><text x="66" y="107">SET</text></g><path d="M90 103h10"/><path d="M100 103h10"/><g class="terminal"><path d="M110 103h0"/><path d="M196 103h0"/><rect x="110" y="92" width="86" height="22" rx="10" ry="10"/><text x="153" y="107">DEFAULT</text></g></g><path d="M196 103a10 10 0 0 0 10 -10v-70a10 10 0 0 1 10 -10"/><path d="M22 13a10 10 0 0 1 10 10v100a10 10 0 0 0 10 10"/><g><path d="M42 133h0"/><path d="M181 133h15"/><g class="terminal"><path d="M42 133h0"/><path d="M84 133h0"/><rect x="42" y="122" width="42" height="22" rx="10" ry="10"/><text x="63" y="137">NO</text></g><path d="M84 133h10"/><path d="M94 133h10"/><g class="terminal"><path d="M104 133h0"/><path d="M181 133h0"/><rect x="104" y="122" width="77" height="22" rx="10" ry="10"/><text x="142.5" y="137">ACTION</text></g></g><path d="M196 133a10 10 0 0 0 10 -10v-100a10 10 0 0 1 10 -10"/></g><path d="M216 13h4m0-4v8l16-8v8Z" class="start-end"/></g></svg></dd></dl></div><div hidden=""><pre><code class="hljs language-ebnf"><style data-emotion="css 1qhimia">.css-1qhimia{margin-right:3rem;overflow:auto;}</style><div class="MuiBox-root css-1qhimia"><span class="hljs-attribute">ForeignKeyDef</span> ::= ( <span class="hljs-string">'CONSTRAINT'</span> Identifier )? <span class="hljs-string">'FOREIGN'</span> <span class="hljs-string">'KEY'</span> Identifier? <span class="hljs-string">'('</span> ColumnName ( <span class="hljs-string">','</span> ColumnName )* <span class="hljs-string">')'</span> <span class="hljs-string">'REFERENCES'</span> TableName <span class="hljs-string">'('</span> ColumnName ( <span class="hljs-string">','</span> ColumnName )* <span class="hljs-string">')'</span> ( <span class="hljs-string">'ON'</span> <span class="hljs-string">'DELETE'</span> ReferenceOption )? ( <span class="hljs-string">'ON'</span> <span class="hljs-string">'UPDATE'</span> ReferenceOption )? ReferenceOption ::= <span class="hljs-string">'RESTRICT'</span> | <span class="hljs-string">'CASCADE'</span> | <span class="hljs-string">'SET'</span> <span class="hljs-string">'NULL'</span> | <span class="hljs-string">'SET'</span> <span class="hljs-string">'DEFAULT'</span> | <span class="hljs-string">'NO'</span> <span class="hljs-string">'ACTION'</span> </div><style data-emotion="css ux9q70">.css-ux9q70{text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:2.4rem;background:transparent;border:unset;}.css-ux9q70:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-ux9q70:hover{background-color:transparent;}}.css-ux9q70.Mui-disabled{background-color:transparent;color:rgba(0, 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0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:2.4rem;background:transparent;border:unset;}.css-1rmx1rm::-moz-focus-inner{border-style:none;}.css-1rmx1rm.Mui-disabled{pointer-events:none;cursor:default;}@media print{.css-1rmx1rm{-webkit-print-color-adjust:exact;color-adjust:exact;}}.css-1rmx1rm:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-1rmx1rm:hover{background-color:transparent;}}.css-1rmx1rm.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><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 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fxo539">.css-fxo539{display:-webkit-inline-box;display:-webkit-inline-flex;display:-ms-inline-flexbox;display:inline-flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;-webkit-box-pack:center;-ms-flex-pack:center;-webkit-justify-content:center;justify-content:center;position:relative;box-sizing:border-box;-webkit-tap-highlight-color:transparent;background-color:transparent;outline:0;border:0;margin:0;border-radius:0;padding:0;cursor:pointer;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none;vertical-align:middle;-moz-appearance:none;-webkit-appearance:none;-webkit-text-decoration:none;text-decoration:none;color:inherit;text-align:center;-webkit-flex:0 0 auto;-ms-flex:0 0 auto;flex:0 0 auto;font-size:1.5rem;padding:8px;border-radius:50%;overflow:visible;color:rgba(0, 0, 0, 0.54);-webkit-transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;transition:background-color 150ms cubic-bezier(0.4, 0, 0.2, 1) 0ms;padding:5px;font-size:1.125rem;top:0.625rem;right:0.625rem;background:transparent;border:unset;}.css-fxo539::-moz-focus-inner{border-style:none;}.css-fxo539.Mui-disabled{pointer-events:none;cursor:default;}@media print{.css-fxo539{-webkit-print-color-adjust:exact;color-adjust:exact;}}.css-fxo539:hover{background-color:rgba(0, 0, 0, 0.04);}@media (hover: none){.css-fxo539:hover{background-color:transparent;}}.css-fxo539.Mui-disabled{background-color:transparent;color:rgba(0, 0, 0, 0.26);}</style><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre></div></div><h2 id="naming" style="position:relative"><a href="#naming" aria-label="naming permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Naming</h2><p>The naming of a foreign key follows the following rules:</p><ul><li>If a name is specified in <code>CONSTRAINT identifier</code>, the specified name is used.</li><li>If no name is specified in <code>CONSTRAINT identifier</code>, but a name is specified in <code>FOREIGN KEY identifier</code>, the name specified in the <code>FOREIGN KEY identifier</code> is used.</li><li>If neither <code>CONSTRAINT identifier</code> nor <code>FOREIGN KEY identifier</code> specifies a name, a name is automatically generated, such as <code>fk_1</code>, <code>fk_2</code>, and <code>fk_3</code>.</li><li>The foreign key name must be unique in the current table. Otherwise, an error <code>ERROR 1826: Duplicate foreign key constraint name 'fk'</code> is reported when the foreign key is created.</li></ul><h2 id="restrictions" style="position:relative"><a href="#restrictions" aria-label="restrictions permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Restrictions</h2><p>When creating a foreign key, the following conditions must be met:</p><ul><li><p>Neither the parent table nor the child table is a temporary table.</p></li><li><p>The user has the <code>REFERENCES</code> privilege on the parent table.</p></li><li><p>The columns referenced by the foreign key in the parent table and the child table are of the same data type and have the same size, precision, length, character set, and collation.</p></li><li><p>The columns in the foreign key cannot reference themselves.</p></li><li><p>The columns in the foreign key and the columns in the referenced parent table have the same index, and the order of the columns in the index matches that in the foreign key. This is to use the index to avoid full table scans when performing foreign key constraint checks.</p><ul><li>If there is no corresponding foreign key index in the parent table, an error <code>ERROR 1822: Failed to add the foreign key constraint. Missing index for constraint 'fk' in the referenced table 't'</code> is reported.</li><li>If there is no corresponding foreign key index in the child table, an index is automatically created with the same name as the foreign key.</li></ul></li><li><p>It is not supported to create a foreign key on a column of the <code>BLOB</code> or <code>TEXT</code> type.</p></li><li><p>It is not supported to create a foreign key on a partitioned table.</p></li><li><p>It is not supported to create a foreign key on a virtual generated column.</p></li></ul><h2 id="reference-operations" style="position:relative"><a href="#reference-operations" aria-label="reference operations permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Reference operations</h2><p>If an <code>UPDATE</code> or <code>DELETE</code> operation affects a foreign key value in the parent table, the corresponding foreign key value in the child table is determined by the reference operation defined by the <code>ON UPDATE</code> or <code>ON DELETE</code> clause in the foreign key definition. The reference operations include the following:</p><ul><li><code>CASCADE</code>: automatically updates or deletes the matching rows in the child table when the <code>UPDATE</code> or <code>DELETE</code> operation affects the parent table. The cascade operation is performed in a depth-first manner.</li><li><code>SET NULL</code>: automatically sets the matching foreign key columns in the child table to <code>NULL</code> when the <code>UPDATE</code> or <code>DELETE</code> operation affects the parent table.</li><li><code>RESTRICT</code>: denies the <code>UPDATE</code> or <code>DELETE</code> operation if the child table contains matching rows.</li><li><code>NO ACTION</code>: the same as <code>RESTRICT</code>.</li><li><code>SET DEFAULT</code>: the same as <code>RESTRICT</code>.</li></ul><p>If there is no matching foreign key value in the parent table, the <code>INSERT</code> or <code>UPDATE</code> operation on the child table is denied.</p><p>If the foreign key definition does not specify <code>ON DELETE</code> or <code>ON UPDATE</code>, the default behavior is <code>NO ACTION</code>.</p><p>If the foreign key is defined on a <code>STORED GENERATED COLUMN</code>, the <code>CASCADE</code>, <code>SET NULL</code>, and <code>SET DEFAULT</code> references are not supported.</p><h2 id="usage-examples-of-foreign-keys" style="position:relative"><a href="#usage-examples-of-foreign-keys" aria-label="usage examples of foreign keys permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Usage examples of foreign keys</h2><p>The following example uses a single-column foreign key to associate the parent table and the child table:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> parent ( id <span class="hljs-type">INT</span> KEY <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child ( id <span class="hljs-type">INT</span>, pid <span class="hljs-type">INT</span>, INDEX idx_pid (pid), <span class="hljs-keyword">FOREIGN</span> KEY (pid) <span class="hljs-keyword">REFERENCES</span> parent(id) <span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> CASCADE </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>The following is a more complex example where the <code>product_order</code> table has two foreign keys that reference the other two tables. One foreign key references two indexes on the <code>product</code> table, and the other references a single index on the <code>customer</code> table:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> product ( category <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>, id <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>, price <span class="hljs-type">DECIMAL</span>(<span class="hljs-number">20</span>,<span class="hljs-number">10</span>), <span class="hljs-keyword">PRIMARY</span> KEY(category, id) <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> customer ( id <span class="hljs-type">INT</span> KEY <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> product_order ( id <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span> AUTO_INCREMENT, product_category <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>, product_id <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>, customer_id <span class="hljs-type">INT</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>, <span class="hljs-keyword">PRIMARY</span> KEY(id), INDEX (product_category, product_id), INDEX (customer_id), <span class="hljs-keyword">FOREIGN</span> KEY (product_category, product_id) <span class="hljs-keyword">REFERENCES</span> product(category, id) <span class="hljs-keyword">ON</span> <span class="hljs-keyword">UPDATE</span> CASCADE <span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> RESTRICT, <span class="hljs-keyword">FOREIGN</span> KEY (customer_id) <span class="hljs-keyword">REFERENCES</span> customer(id) </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h2 id="create-a-foreign-key-constraint" style="position:relative"><a href="#create-a-foreign-key-constraint" aria-label="create a foreign key constraint permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Create a foreign key constraint</h2><p>To create a foreign key constraint, you can use the following <code>ALTER TABLE</code> statement:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">ALTER</span> <span class="hljs-keyword">TABLE</span> table_name <span class="hljs-keyword">ADD</span> [<span class="hljs-keyword">CONSTRAINT</span> [identifier]] <span class="hljs-keyword">FOREIGN</span> KEY [identifier] (col_name, ...) <span class="hljs-keyword">REFERENCES</span> tbl_name (col_name,...) [<span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> reference_option] [<span class="hljs-keyword">ON</span> <span class="hljs-keyword">UPDATE</span> reference_option] </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>The foreign key can be self-referencing, that is, referencing the same table. When you add a foreign key constraint to a table using <code>ALTER TABLE</code>, you need to first create an index on the parent table column that the foreign key references.</p><h2 id="delete-a-foreign-key-constraint" style="position:relative"><a href="#delete-a-foreign-key-constraint" aria-label="delete a foreign key constraint permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Delete a foreign key constraint</h2><p>To delete a foreign key constraint, you can use the following <code>ALTER TABLE</code> statement:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">ALTER</span> <span class="hljs-keyword">TABLE</span> table_name <span class="hljs-keyword">DROP</span> <span class="hljs-keyword">FOREIGN</span> KEY fk_identifier; </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>If the foreign key constraint is named when it is created, you can reference the name to delete the foreign key constraint. Otherwise, you have to use the constraint name automatically generated to delete the constraint. You can use <code>SHOW CREATE TABLE</code> to view the foreign key name:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SHOW</span> <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child\G <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> <span class="hljs-number">1.</span> <span class="hljs-type">row</span> <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> <span class="hljs-keyword">Table</span>: child <span class="hljs-keyword">Create</span> <span class="hljs-keyword">Table</span>: <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> `child` ( `id` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, `pid` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, KEY `idx_pid` (`pid`), <span class="hljs-keyword">CONSTRAINT</span> `fk_1` <span class="hljs-keyword">FOREIGN</span> KEY (`pid`) <span class="hljs-keyword">REFERENCES</span> `test`.`parent` (`id`) <span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> CASCADE ) ENGINE<span class="hljs-operator">=</span>InnoDB <span class="hljs-keyword">DEFAULT</span> CHARSET<span class="hljs-operator">=</span>utf8mb4 <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_bin </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="foreign-key-constraint-check" style="position:relative"><a href="#foreign-key-constraint-check" aria-label="foreign key constraint check permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Foreign key constraint check</h2><p>TiDB supports foreign key constraint check, which is controlled by the system variable <a href="/tidb/stable/system-variables#foreign_key_checks"><code>foreign_key_checks</code></a>. By default, this variable is set to <code>ON</code>, meaning that the foreign key constraint check is enabled. This variable has two scopes: <code>GLOBAL</code> and <code>SESSION</code>. Keeping this variable enabled can ensure the integrity of foreign key reference relationships.</p><p>The effect of disabling foreign key constraint check is as follows:</p><ul><li>When you delete a parent table referenced by a foreign key, the deletion can succeed only when the foreign key constraint check is disabled.</li><li>When you import data to a database, the order of creating tables might be different from the foreign key dependency order, which might cause the creation of tables to fail. Only when the foreign key constraint check is disabled can the tables be created successfully. In addition, disabling the foreign key constraint check can speed up data import.</li><li>When you import data to a database, if the data of the child table is imported first, an error will be reported. Only when the foreign key constraint check is disabled can the data of the child table be imported successfully.</li><li>If an <code>ALTER TABLE</code> operation to be executed involves a change of the foreign key, this operation succeeds only when the foreign key constraint check is disabled.</li></ul><p>When the foreign key constraint check is disabled, the foreign key constraint check and reference operation are not executed, except for the following scenarios:</p><ul><li>If the execution of <code>ALTER TABLE</code> might result in wrong definition of the foreign key, an error is still reported during the execution.</li><li>When deleting the index required by the foreign key, you should delete the foreign key first. Otherwise, an error is reported.</li><li>When you create a foreign key but it does not meet related conditions or restrictions, an error is reported.</li></ul><h2 id="locking" style="position:relative"><a href="#locking" aria-label="locking permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Locking</h2><p>When <code>INSERT</code> or <code>UPDATE</code> a child table, the foreign key constraint checks whether the corresponding foreign key value exists in the parent table, and locks the row in the parent table to avoid the foreign key value being deleted by other operations violating the foreign key constraint. The locking behavior is equivalent to performing a <code>SELECT FOR UPDATE</code> operation on the row where the foreign key value is located in the parent table.</p><p>Because TiDB currently does not support <code>LOCK IN SHARE MODE</code>, if a child table accepts a large number of concurrent writes and most of the referenced foreign key values are the same, there might be serious locking conflicts. It is recommended to disable <a href="/tidb/stable/system-variables#foreign_key_checks"><code>foreign_key_checks</code></a> when writing a large number of child table data.</p><h2 id="definition-and-metadata-of-foreign-keys" style="position:relative"><a href="#definition-and-metadata-of-foreign-keys" aria-label="definition and metadata of foreign keys permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Definition and metadata of foreign keys</h2><p>To view the definition of a foreign key constraint, execute the <a href="/tidb/stable/sql-statement-show-create-table"><code>SHOW CREATE TABLE</code></a> statement:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SHOW</span> <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child\G <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> <span class="hljs-number">1.</span> <span class="hljs-type">row</span> <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> <span class="hljs-keyword">Table</span>: child <span class="hljs-keyword">Create</span> <span class="hljs-keyword">Table</span>: <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> `child` ( `id` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, `pid` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, KEY `idx_pid` (`pid`), <span class="hljs-keyword">CONSTRAINT</span> `fk_1` <span class="hljs-keyword">FOREIGN</span> KEY (`pid`) <span class="hljs-keyword">REFERENCES</span> `test`.`parent` (`id`) <span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> CASCADE ) ENGINE<span class="hljs-operator">=</span>InnoDB <span class="hljs-keyword">DEFAULT</span> CHARSET<span class="hljs-operator">=</span>utf8mb4 <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_bin </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>You can also get information about foreign keys using either of the following system tables:</p><ul><li><a href="/tidb/stable/information-schema-key-column-usage"><code>INFORMATION_SCHEMA.KEY_COLUMN_USAGE</code></a></li><li><a href="/tidb/stable/information-schema-table-constraints"><code>INFORMATION_SCHEMA.TABLE_CONSTRAINTS</code></a></li><li><a href="/tidb/stable/information-schema-referential-constraints"><code>INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS</code></a></li></ul><p>The following provides examples:</p><p>Get information about foreign keys from the <code>INFORMATION_SCHEMA.KEY_COLUMN_USAGE</code> system table:</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> TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME <span class="hljs-keyword">FROM</span> INFORMATION_SCHEMA.KEY_COLUMN_USAGE <span class="hljs-keyword">WHERE</span> REFERENCED_TABLE_SCHEMA <span class="hljs-keyword">IS</span> <span class="hljs-keyword">NOT</span> <span class="hljs-keyword">NULL</span>; <span class="hljs-operator">+</span><span class="hljs-comment">--------------+---------------+------------------+-----------------+</span> <span class="hljs-operator">|</span> TABLE_SCHEMA <span class="hljs-operator">|</span> TABLE_NAME <span class="hljs-operator">|</span> COLUMN_NAME <span class="hljs-operator">|</span> CONSTRAINT_NAME <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">--------------+---------------+------------------+-----------------+</span> <span class="hljs-operator">|</span> test <span class="hljs-operator">|</span> child <span class="hljs-operator">|</span> pid <span class="hljs-operator">|</span> fk_1 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test <span class="hljs-operator">|</span> product_order <span class="hljs-operator">|</span> product_category <span class="hljs-operator">|</span> fk_1 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test <span class="hljs-operator">|</span> product_order <span class="hljs-operator">|</span> product_id <span class="hljs-operator">|</span> fk_1 <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> test <span class="hljs-operator">|</span> product_order <span class="hljs-operator">|</span> customer_id <span class="hljs-operator">|</span> fk_2 <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>Get information about foreign keys from the <code>INFORMATION_SCHEMA.TABLE_CONSTRAINTS</code> system table:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> INFORMATION_SCHEMA.TABLE_CONSTRAINTS <span class="hljs-keyword">WHERE</span> CONSTRAINT_TYPE<span class="hljs-operator">=</span><span class="hljs-string">'FOREIGN KEY'</span>\G <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span>[ <span class="hljs-number">1.</span> <span class="hljs-type">row</span> ]<span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> CONSTRAINT_CATALOG <span class="hljs-operator">|</span> def CONSTRAINT_SCHEMA <span class="hljs-operator">|</span> test CONSTRAINT_NAME <span class="hljs-operator">|</span> fk_1 TABLE_SCHEMA <span class="hljs-operator">|</span> test TABLE_NAME <span class="hljs-operator">|</span> child CONSTRAINT_TYPE <span class="hljs-operator">|</span> <span class="hljs-keyword">FOREIGN</span> KEY </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>Get information about foreign keys from the <code>INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS</code> system table:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SELECT</span> <span class="hljs-operator">*</span> <span class="hljs-keyword">FROM</span> INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS\G <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span>[ <span class="hljs-number">1.</span> <span class="hljs-type">row</span> ]<span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> CONSTRAINT_CATALOG <span class="hljs-operator">|</span> def CONSTRAINT_SCHEMA <span class="hljs-operator">|</span> test CONSTRAINT_NAME <span class="hljs-operator">|</span> fk_1 UNIQUE_CONSTRAINT_CATALOG <span class="hljs-operator">|</span> def UNIQUE_CONSTRAINT_SCHEMA <span class="hljs-operator">|</span> test UNIQUE_CONSTRAINT_NAME <span class="hljs-operator">|</span> <span class="hljs-keyword">PRIMARY</span> MATCH_OPTION <span class="hljs-operator">|</span> <span class="hljs-keyword">NONE</span> UPDATE_RULE <span class="hljs-operator">|</span> <span class="hljs-keyword">NO</span> ACTION DELETE_RULE <span class="hljs-operator">|</span> CASCADE TABLE_NAME <span class="hljs-operator">|</span> child REFERENCED_TABLE_NAME <span class="hljs-operator">|</span> parent </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="view-execution-plans-with-foreign-keys" style="position:relative"><a href="#view-execution-plans-with-foreign-keys" aria-label="view execution plans with foreign keys permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>View execution plans with foreign keys</h2><p>You can use the <code>EXPLAIN</code> statement to view execution plans. The <code>Foreign_Key_Check</code> operator performs the foreign key constraint check on DML statements that are executed.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> explain <span class="hljs-keyword">insert</span> <span class="hljs-keyword">into</span> child <span class="hljs-keyword">values</span> (<span class="hljs-number">1</span>,<span class="hljs-number">1</span>); <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------+---------+------+---------------+-------------------------------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-----------------------+---------+------+---------------+-------------------------------+</span> <span class="hljs-operator">|</span> Insert_1 <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Foreign_Key_Check_3 <span class="hljs-operator">|</span> <span class="hljs-number">0.00</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:parent <span class="hljs-operator">|</span> foreign_key:fk_1, check_exist <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>You can use the <code>EXPLAIN ANALYZE</code> statement to view the execution of the foreign key reference behavior. The <code>Foreign_Key_Cascade</code> operator performs foreign key referencing for DML statements that are executed.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> explain analyze <span class="hljs-keyword">delete</span> <span class="hljs-keyword">from</span> parent <span class="hljs-keyword">where</span> id <span class="hljs-operator">=</span> <span class="hljs-number">1</span>; <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+---------+---------+-----------+---------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+-----------+------+</span> <span class="hljs-operator">|</span> id <span class="hljs-operator">|</span> estRows <span class="hljs-operator">|</span> actRows <span class="hljs-operator">|</span> task <span class="hljs-operator">|</span> access object <span class="hljs-operator">|</span> execution info <span class="hljs-operator">|</span> operator info <span class="hljs-operator">|</span> memory <span class="hljs-operator">|</span> disk <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">----------------------------------+---------+---------+-----------+---------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------+-----------+------+</span> <span class="hljs-operator">|</span> Delete_2 <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">117.3</span>µs, loops:<span class="hljs-number">1</span> <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-number">380</span> Bytes <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─Point_Get_1 <span class="hljs-operator">|</span> <span class="hljs-number">1.00</span> <span class="hljs-operator">|</span> <span class="hljs-number">1</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:parent <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">63.6</span>µs, loops:<span class="hljs-number">2</span>, <span class="hljs-keyword">Get</span>:{num_rpc:<span class="hljs-number">1</span>, total_time:<span class="hljs-number">29.9</span>µs} <span class="hljs-operator">|</span> handle:<span class="hljs-number">1</span> <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Foreign_Key_Cascade_3 <span class="hljs-operator">|</span> <span class="hljs-number">0.00</span> <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:child, index:idx_pid <span class="hljs-operator">|</span> total:<span class="hljs-number">1.28</span>ms, foreign_keys:<span class="hljs-number">1</span> <span class="hljs-operator">|</span> foreign_key:fk_1, on_delete:CASCADE <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─Delete_7 <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-number">0</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">904.8</span>µs, loops:<span class="hljs-number">1</span> <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-number">1.11</span> KB <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─IndexLookUp_11 <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> <span class="hljs-number">1</span> <span class="hljs-operator">|</span> root <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">869.5</span>µs, loops:<span class="hljs-number">2</span>, index_task: {total_time: <span class="hljs-number">371.1</span>µs, fetch_handle: <span class="hljs-number">357.3</span>µs, build: <span class="hljs-number">1.25</span>µs, wait: <span class="hljs-number">12.5</span>µs}, table_task: {total_time: <span class="hljs-number">382.6</span>µs, num: <span class="hljs-number">1</span>, concurrency: <span class="hljs-number">5</span>} <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> <span class="hljs-number">9.13</span> KB <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> ├─IndexRangeScan_9(Build) <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> <span class="hljs-number">1</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:child, index:idx_pid(pid) <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">351.2</span>µs, loops:<span class="hljs-number">3</span>, cop_task: {num: <span class="hljs-number">1</span>, max: <span class="hljs-number">282.3</span>µs, proc_keys: <span class="hljs-number">0</span>, rpc_num: <span class="hljs-number">1</span>, rpc_time: <span class="hljs-number">263</span>µs, copr_cache_hit_ratio: <span class="hljs-number">0.00</span>, distsql_concurrency: <span class="hljs-number">15</span>}, tikv_task:{<span class="hljs-type">time</span>:<span class="hljs-number">220.2</span>µs, loops:<span class="hljs-number">0</span>} <span class="hljs-operator">|</span> <span class="hljs-keyword">range</span>:[<span class="hljs-number">1</span>,<span class="hljs-number">1</span>], keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> <span class="hljs-operator">|</span> └─TableRowIDScan_10(Probe) <span class="hljs-operator">|</span> <span class="hljs-number">10.00</span> <span class="hljs-operator">|</span> <span class="hljs-number">1</span> <span class="hljs-operator">|</span> cop[tikv] <span class="hljs-operator">|</span> <span class="hljs-keyword">table</span>:child <span class="hljs-operator">|</span> <span class="hljs-type">time</span>:<span class="hljs-number">223.9</span>µs, loops:<span class="hljs-number">2</span>, cop_task: {num: <span class="hljs-number">1</span>, max: <span class="hljs-number">168.8</span>µs, proc_keys: <span class="hljs-number">0</span>, rpc_num: <span class="hljs-number">1</span>, rpc_time: <span class="hljs-number">154.5</span>µs, copr_cache_hit_ratio: <span class="hljs-number">0.00</span>, distsql_concurrency: <span class="hljs-number">15</span>}, tikv_task:{<span class="hljs-type">time</span>:<span class="hljs-number">145.6</span>µs, loops:<span class="hljs-number">0</span>} <span class="hljs-operator">|</span> keep <span class="hljs-keyword">order</span>:<span class="hljs-literal">false</span>, stats:pseudo <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <span class="hljs-operator">|</span> N<span class="hljs-operator">/</span>A <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><h2 id="compatibility" style="position:relative"><a href="#compatibility" aria-label="compatibility permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Compatibility</h2><h3 id="compatibility-between-tidb-versions" style="position:relative"><a href="#compatibility-between-tidb-versions" aria-label="compatibility between tidb versions permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Compatibility between TiDB versions</h3><p>Before v6.6.0, TiDB supports the syntax of creating foreign keys, but the created foreign keys are ineffective. If you upgrade a TiDB cluster created before v6.6.0 to v6.6.0 or later, the foreign keys created before the upgrade are still ineffective. Only the foreign keys created in v6.6.0 or later versions are effective. You can delete the invalid foreign key and create a new one to make the foreign key constraints effective. You can use the <code>SHOW CREATE TABLE</code> statement to check whether the foreign keys are effective. The invalid foreign key has a <code>/* FOREIGN KEY INVALID */</code> comment.</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia">mysql<span class="hljs-operator">&gt;</span> <span class="hljs-keyword">SHOW</span> <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child\G <span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span>[ <span class="hljs-number">1.</span> <span class="hljs-type">row</span> ]<span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span><span class="hljs-operator">*</span> <span class="hljs-keyword">Table</span> <span class="hljs-operator">|</span> child <span class="hljs-keyword">Create</span> <span class="hljs-keyword">Table</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> `child` ( `id` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, `pid` <span class="hljs-type">int</span>(<span class="hljs-number">11</span>) <span class="hljs-keyword">DEFAULT</span> <span class="hljs-keyword">NULL</span>, KEY `idx_pid` (`pid`), <span class="hljs-keyword">CONSTRAINT</span> `fk_1` <span class="hljs-keyword">FOREIGN</span> KEY (`pid`) <span class="hljs-keyword">REFERENCES</span> `test`.`parent` (`id`) <span class="hljs-keyword">ON</span> <span class="hljs-keyword">DELETE</span> CASCADE <span class="hljs-comment">/* FOREIGN KEY INVALID */</span> ) ENGINE<span class="hljs-operator">=</span>InnoDB <span class="hljs-keyword">DEFAULT</span> CHARSET<span class="hljs-operator">=</span>utf8mb4 <span class="hljs-keyword">COLLATE</span><span class="hljs-operator">=</span>utf8mb4_bin </div><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-1rmx1rm" tabindex="0" type="button" aria-label="Toggle code wrap"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="WrapTextIcon"><path d="M4 19h6v-2H4v2zM20 5H4v2h16V5zm-3 6H4v2h13.25c1.1 0 2 .9 2 2s-.9 2-2 2H15v-2l-3 3 3 3v-2h2c2.21 0 4-1.79 4-4s-1.79-4-4-4z"/></svg></button><button class="MuiButtonBase-root MuiIconButton-root MuiIconButton-sizeSmall css-fxo539" tabindex="0" type="button" aria-label="copy"><svg class="MuiSvgIcon-root MuiSvgIcon-fontSizeInherit css-1cw4hi4" focusable="false" aria-hidden="true" viewbox="0 0 24 24" data-testid="ContentCopyIcon"><path d="M16 1H4c-1.1 0-2 .9-2 2v14h2V3h12V1zm3 4H8c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h11c1.1 0 2-.9 2-2V7c0-1.1-.9-2-2-2zm0 16H8V7h11v14z"/></svg></button></code></pre><h3 id="compatibility-with-tidb-tools" style="position:relative"><a href="#compatibility-with-tidb-tools" aria-label="compatibility with tidb tools permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Compatibility with TiDB tools</h3><ul><li><a href="/tidb/stable/tidb-binlog-overview">TiDB Binlog</a> does not support foreign keys.</li><li><a href="/tidb/stable/dm-overview">DM</a> does not support foreign keys. DM disables the <a href="/tidb/stable/system-variables#foreign_key_checks"><code>foreign_key_checks</code></a> of the downstream TiDB when replicating data to TiDB. Therefore, the cascading operations caused by foreign keys are not replicated from the upstream to the downstream, which might cause data inconsistency.</li><li><a href="/tidb/stable/ticdc-overview">TiCDC</a> v6.6.0 is compatible with foreign keys. The previous versions of TiCDC might report an error when replicating tables with foreign keys. It is recommended to disable the <code>foreign_key_checks</code> of the downstream TiDB cluster when using a TiCDC version earlier than v6.6.0.</li><li><a href="/tidb/stable/backup-and-restore-overview">BR</a> v6.6.0 is compatible with foreign keys. The previous versions of BR might report an error when restoring tables with foreign keys to a v6.6.0 or later cluster. It is recommended to disable the <code>foreign_key_checks</code> of the downstream TiDB cluster before restoring the cluster when using a BR earlier than v6.6.0.</li><li>When you use <a href="/tidb/stable/tidb-lightning-overview">TiDB Lightning</a>, it is recommended to disable the <code>foreign_key_checks</code> of the downstream TiDB cluster before importing data.</li></ul><ul><li><a href="https://docs.pingcap.com/tidb/stable/dumpling-overview" target="_blank" referrerpolicy="no-referrer-when-downgrade">Dumpling</a> is compatible with foreign keys.</li></ul><ul><li>When you use <a href="/tidb/stable/sync-diff-inspector-overview">sync-diff-inspector</a> to compare data between the upstream and downstream databases, if the database versions are different and there is <a href="#compatibility-between-tidb-versions">an invalid foreign key in the downstream TiDB</a>, sync-diff-inspector might report a table schema inconsistent error. This is because TiDB v6.6.0 adds a <code>/* FOREIGN KEY INVALID */</code> comment for the invalid foreign key.</li></ul><h3 id="compatibility-with-mysql" style="position:relative"><a href="#compatibility-with-mysql" aria-label="compatibility with mysql permalink" class="anchor before"><svg aria-hidden="true" focusable="false" height="16" version="1.1" viewbox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"/></svg></a>Compatibility with MySQL</h3><p>When you create a foreign key without specifying a name, the name generated by TiDB is different from that generated by MySQL. For example, the foreign key name generated by TiDB is <code>fk_1</code>, <code>fk_2</code>, and <code>fk_3</code>, while the foreign key name generated by MySQL is <code>table_name_ibfk_1</code>, <code>table_name_ibfk_2</code>, and <code>table_name_ibfk_3</code>.</p><p>Both MySQL and TiDB parse but ignore "inline <code>REFERENCES</code> specifications". Only <code>REFERENCES</code> specifications that are part of <code>FOREIGN KEY</code> definitions are checked and enforced. The following example creates a foreign key constraint using a <code>REFERENCES</code> clause:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> parent ( id <span class="hljs-type">INT</span> KEY <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child ( id <span class="hljs-type">INT</span>, pid <span class="hljs-type">INT</span> <span class="hljs-keyword">REFERENCES</span> parent(id) <span class="hljs-keyword">SHOW</span> <span class="hljs-keyword">CREATE</span> <span class="hljs-keyword">TABLE</span> child; </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>The output shows that the <code>child</code> table does not contain any foreign keys:</p><pre><code class="hljs language-sql"><div class="MuiBox-root css-1qhimia"><span class="hljs-operator">+</span><span class="hljs-comment">-------+-------------------------------------------------------------+</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">Table</span> <span class="hljs-operator">|</span> <span class="hljs-keyword">Create</span> <span class="hljs-keyword">Table</span> <span class="hljs-operator">|</span> <span class="hljs-operator">+</span><span class="hljs-comment">-------+-------------------------------------------------------------+</span>