回顾一下some any all 用法
userinfo表里面有100条数据,其中一个用户名为qixuejia.
1.some,any用法一样(不知道有没有其他的不同)
select count(*) from userinfo
where 'qixuejia' <> some(select userid from userinfo)
where 条件成立 该条语句返回100.
2.all
select count(*) from userinfo
where 'qixuejia' <> all(select userid from userinfo)
该where语句判断qixuejia不等于所有的userid,返回否.
所以该语句返回0
3.select count(*) from userinfo
where 'qixuejia'in (select userid from userinfo)
返回100
4.select count(*) from userinfo
where userid='qixuejia'
返回1
5.select count(*) from userinfo
where 'qixuejia' not in (select userid from userinfo)
返回0
