具有公共成员的SQL查找集（关系除法）

我认为这也应该起作用

select distinct g.GroupID, c.ClassIDfrom @Groups g    left join @Classes c on g.TagID = c.TagIDwhere not exists (    select *    from @Groups g2    where g2.GroupID = g.GroupID        and g2.TagID not in ( select TagID from @Classes c2 where c2.ClassID = c.ClassID        )    ) or c.ClassID is null