我有一张表给朋友们
PLAYER_ID FRIEND_ID ---------------------- 1 2 1 3 // 1 knows 3 3 1 // 3 knows 1 2 4
如何为给定玩家创建一个包含那些熟人（彼此了解）的视图？
PLAYER_ID FRIEND_ID ---------------------- 1 3 3 1
谢谢你。
这是所需的选择：
select t1.PLAYER_id, t1.FRIEND_ID from tablename t1 inner join tablename t2 on t1.PLAYER_id = t2.FRIEND_ID and t2.PLAYER_id = t1.FRIEND_ID
