How to query users who have the same friends and are not friends in a friend table

In a friend table, how does one query User uid and friend ID that have the same friends and are not friends? in another table, how does one query in a friend table is the same as the user ID? users of friends who are not friends of their own, the friend table has at least two fields: user_id and friend_ I. how can I query users who have the same friends and are not friends in a friend table?


Uid and Friend ID are both in another table.
How to query users who have the same friends and are not friends in a friend table?

------ Solution --------------------
The friend table has at least two fields: user_id and friend_id.
1. First, find out your friend: select friend_id from friend where user_id = "zhangshan ";
2. select distinct user_id from friend where friend_id in (select friend_id from friend where user_id = "zhangshan") and user_id! = "Zhangshan" and user_id not in (select friend_id from friend where user_id = "zhangshan ");