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什么是最左前缀原则？什么是最左匹配原则
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#IAJKYW
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2024-08-13 10:10
<p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">顾名思义，就是最左优先，在创建多列索引时，要根据业务需求，where子句中使用最频繁的一列放在最左边。 </span></p><p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">最左前缀匹配原则，非常重要的原则，mysql会一直向右匹配直到遇到范围查询 (>、<、between、like)就停止匹配，比如a = 1 and b = 2 and c > 3 and d = 4 如果建立(a,b,c,d)顺序的索引，d是用不到索引的，如果建立(a,b,d,c)的索引则都可以用到，a,b,d的顺序可以任意调整。 </span></p><p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">=和in可以乱序，比如a = 1 and b = 2 and c = 3 建立(a,b,c)索引可以任意顺序，mysql的查询优化器会帮你优化成索引可以识别的形式 </span></p>
<p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">顾名思义，就是最左优先，在创建多列索引时，要根据业务需求，where子句中使用最频繁的一列放在最左边。 </span></p><p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">最左前缀匹配原则，非常重要的原则，mysql会一直向右匹配直到遇到范围查询 (>、<、between、like)就停止匹配，比如a = 1 and b = 2 and c > 3 and d = 4 如果建立(a,b,c,d)顺序的索引，d是用不到索引的，如果建立(a,b,d,c)的索引则都可以用到，a,b,d的顺序可以任意调整。 </span></p><p><span style="color: rgb(0, 0, 0); font-family: 微软雅黑;">=和in可以乱序，比如a = 1 and b = 2 and c = 3 建立(a,b,c)索引可以任意顺序，mysql的查询优化器会帮你优化成索引可以识别的形式 </span></p>
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