关系司：我整除

Question

遇到下列问题就来了：

编写一个查询，找到完全相同的朋友，另一个用户的所有用户U.

下面是表（和一个SQL小提琴：http://sqlfiddle.com/#!9/457260/1）：

• 用户：
  • USER_ID：诠释
• 友谊：
  • USER_ID：诠释
  • friend_id：诠释

，我有我的查询的问题是，它返回有用户相同的朋友或超过用户U.

SELECT * 
FROM users INNER JOIN friendships ON users.id = friendships.user_id 
WHERE users.id != 1 AND friendships.friend_id IN (
    SELECT DISTINCT friendships.friend_id 
    FROM friendships 
    WHERE friendships.user_id = 1 
) 
GROUP BY users.id 
HAVING COUNT(DISTINCT friendships.friend_id) = (
    SELECT COUNT(DISTINCT friendships.friend_id) 
    FROM friendships 
    WHERE friendships.user_id = 1 
); 

Answer 1

最简单的方法是聚集朋友，然后做比较：

with f as (
     select user_id, array_agg(friend_id order by friend_id) as friends 
     from friendships f 
     group by user_id 
    ) 
select user_id 
from f 
where f.friends = (select friends from f where user_id = 1) and 
     f.user_id <> 1;