sql优化，如何将in换为exists

Posted 2022-04-24 yanpingping

原sql语句

-- 根据权限表查出该用户拥有的所有权限菜单
select * from tb_power where id in(
 select power_id  from  tb_role_power where role_id in(
   select role_id from tb_user_role where userid=1
 )
)

优化后

1 -- 优化
2 select * from tb_power  p where  exists(
3  select power_id  from  tb_role_power rp where  exists(
4    select 1 from tb_user_role ur where userid=1 and ur.role_id=rp.role_id
5  )  and p.id=rp.power_id
6 )