select * from product.login_info where username not in (select username from stat.totaluser)
vs.
select a.* from product.login_info as a left join stat.totaluser as b on a.username = b.username where b.username is null
上面2条sql语句的执行结果集是一样的
原文：https://www.cnblogs.com/printk/p/9830510.html