MySql in子句 效率低下优化

update clear_res set candelete=0 where resid in
(
 select distinct resourceid from att_attentionresult where important=0
);

耗时 365s

优化后

 update clear_res set candelete=0 where resid in
(
  select resourceid from (
    select distinct resourceid from att_attentionresult where important=0
  ) as tmp
);

耗时 1.41s

总结：对于where xxx in 子句效率极其低下问题，经过in的子句外包装一层select xxx from( ... )as tmp 后，极大优化效率。

MySql in子句 效率低下优化

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