Question

not in 转换为linq to sql怎么写？例子：查询没有分配组的用户

三张表User(id,name),Group(id,name),UserRefGroup(userId,groupId)
UserRefGroup在类中不存在

sql语句：select * from User where id not in (select userId from UserRefGroup)

Answer 1

使用not exists
select * from User a where not exists (select 1 from UserRefGroup b where b.userid = a.id)

没明白你的linq to sql是什么意思，莫非要使用连接的形式，如果是的话，那么左连接这样写
select * from User a left join UserRefGroup b
on a.id = b.userid
where b.userid is null
没关联到的就是没分配的。不过建议用not exists

追问

用linq to sql 来写，不用sql语句

Answer 2

楼主，没UserRefGroup entity class怎么用linq查？

var result = from x in User where !(from v in UserRefGroup select v.userId).Contains(x.id) select x;