查询不在另一张表的数据
有a表，ID，name，b表，id，groupid，b表的id和a表的id是主外键关系，如何求出在b表中没有a表的数据。
[解决办法]
select * from b
where not exists(select 1 from a where a.id=b.id)
[解决办法]
declare @a table(id int)
declare @b table(id int)
insert @a select 1 union all select 2
insert @b select 1 union all select 2 union all select 3
select *
from @b b
where not exists(select id from @a where id = b.id)
select *
from @b b
where id not in (select id from @a )
