Home Database Mysql Tutorial 两个 mysql SQL优化技艺

两个 mysql SQL优化技艺

Jun 07, 2016 pm 04:24 PM
mysql sql optimization

两个 mysql SQL优化技巧 1, limit offset 优化 ? ? ? ?mysql SELECT * FROM `bigtable` order by value limit 50,5; ? ? ? ?优化后: ? ? ? ?mysql EXPLAIN SELECT * FROM `bigtable` ? ? ? ? ? ? ? ? INNER JOIN( ? ? ? ? ? ??select id from `bigtable` or

两个 mysql SQL优化技巧

1, limit offset 优化

? ? ? ?mysql >SELECT * FROM `bigtable` order by value limit 50,5;

? ? ? ?优化后:

? ? ? ?mysql >EXPLAIN SELECT * FROM `bigtable`

? ? ? ? ? ? ? ? INNER JOIN(

? ? ? ? ? ??select id from `bigtable` order by value limit 50,5

? ? ? ? ? ? ? ? ?) as lim USING(id);

? ? ? ?说明:通过联结先取得符合条件的主键ID,然后再在原表上查找剩余的行,这样减少了读取无用行中的数据。

? ? ? ?如果事先将limit 分页计算出索引列的准确位置,那么可以使用索引范围扫描,写成这样:

? ? ? mysql >SELECT * FROM `bigtable` where position between 5 and 10 order by position;

? ? ? position 是bigtable 表的一列。

2, 始终使用union all 代替union ,除非需要服务器消除重复的行。

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