where条件字段可以设置索引吗
2023-08-08 分类:百科
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假设有组合索引 index(a,b,c),以下情况不考虑 select * 内容 (覆盖索引)
where a = 3 用到索引 a
where a = 3 and b = 3 用到索引 a,b
where a = 3 and b = 4 and c = 5 用到索引 a,b,c
where b = 3 或者 where b = 3 and c = 4 或者 where c = 4 索引失效
where a = 3 and c = 5 用到索引 a
where a = 3 and b > 4 and c = 5 用到索引a和b,c不能用在范围之后
where a = 3 and b like 'kk%' and c = 4 用到索引a,b,c。
where a = 3 and b like '%kk' and c = 4 使用到 a
where a = 3 and b like '%kk%' and c = 4 用到 a
where a = 3 and b like 'k%kk%' and c = 4 用到a,b,c
切记使用索引字段值的类型必须匹配,否则索引无效。
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