sql优化，如何将in换为exists

原sql语句

?

1 2 3 4 5 6

-- 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

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