Question

我有两个表，一个叫做用户（id,first name,last name...）第二个叫做 follows，其中包含有关哪个用户关注其他用户的数据

下表示例

userId   followerId
6           10
6           2
6           3
8           1
8           2
8           3

如何获取两个用户的共同好友数量

预期结果应该是

first_user second_user num_of_mutual_friends
    83          73               3

Answer 1

WITH firstUser AS (
    SELECT followerId
    FROM followings
    WHERE userId = 6 
)
, secondUser AS (
    SELECT followerId
    FROM followings
    WHERE userId = 8 
)

SELECT COUNT(followerId)
FROM firstUser
INNER JOIN secondUser ON firstUser.followerId = secondUser.followerId

Answer 2

有多种方法可以实现您的愿望，但这应该可以解决问题：

select
  f.userId as first_user,
  s.userId as second_user,
  count(*) as num_of_mutual_friends
from
  followings f
  inner join followings s on s.followerId = f.followerId
                         and s.userId = 6
where
  f.userId = 8
group by
  f.userId,
  s.userId

您可以查看 here 一个工作示例。

Answer 3

从用户加入以下两个：

select u.*
from users
join followings a on a.followerId = u.id
  and a.userid = 6
join followings b on b.followerId = u.id
  and b.userid = 8

Answer 4

您也可以使用子查询来做到这一点。因此，如果您想获取 id 为 8 的用户和 id 为 6 的用户之间相互关注的人数，您可以使用：

解决方案 1：

SELECT COUNT(followerId) AS mutual_followers_count FROM followings WHERE userId = 6 AND followerId IN (SELECT followerId FROM followings WHERE userId = 8)

解决方案 2：

SELECT COUNT(DISTINCT(followerId)) AS mutual_followers_count FROM followings WHERE followerId in (SELECT followerId FROM followings WHERE userId = 6) AND followerId in (SELECT followerId FROM followings WHERE userId = 8)

获取共同好友的Sql查询

4 个答案: