SQL Server 替換 not in 的用法

select * from T_A a (nolock) where a.xh not in (select xh from T_B)

方法1：效果甚微

select * from T_A a (nolock) where not exists (select xh from T_B where xh=a.xh)

方法2：效果比想象的要好。

select * from T_A a (nolock) left join T_B b on b.xh=a.xh where b.xh is null