谈NOT IN和Exists

 表1: test001

select * from test001

表2：test002

select * from test002

执行语句：

select * from test002 where id not in(select id from test001)

居然没有结果？

原因：因为test001表中有id为空

解决方法：

方法一：

select * from test002 where id not in(select id from test001 where id is not null)

方法二：

select * from test002 a where not exists (select 1 from test001 b where b.id=a.id)

参考网址:
http://x-spirit.iteye.com/blog/615603