07索引

微放 / 2024-10-23 / 原文

索引

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索引失效的情况

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所查找的数据在索引中都有就叫覆盖索引

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所以当使用select *时非常容易出现回表查询,性能就会降低

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前缀取多少个,取决于需求,根据需求确定选择性

选择性不重复的个数/总数

使用前缀索引可以降低索引体积,提高索引效率

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