选择同一表中的记录子集

Question

有一个表格显示权限和某些对象的映射，即对象＆＃39; obj1＆＃39;有＆＃39; perm1＆＃39;和＆＃39; perm2＆＃39;权限，＆＃39; obj2＆＃39; - ＆＃39; perm1＆＃39;和＆＃39; perm3＆＃39;。

Permission_id Object_Id
  perm1      |   obj1
  perm2      |   obj1
  perm1      |   obj2
  perm3      |   obj2

问题是：如何获取应用于所有对象的权限子集？即：

Permission_id 
    perm1     

Answer 1

以下为此目的使用计数和聚合：

select permission_id
from permissionobjects po
group by permission_id
having count(distinct object_id) = (select count(distinct object_id) from permissionobjects);