MySQL 对连接表的计数

Question

我有一个用户表，如下(简写):

id (BIGINT)
username (VARCHAR)
recommendedByUserId (BIGINT)

在recommendedByUserId中存储推荐者的ID，这是推荐者的users.id值。这是有效的:

SELECT u.username, recomm.recommCount, recomm.likesCount
FROM users u
INNER JOIN
(
    SELECT recommendedByUserId as rid, COUNT(*) as recommCount, SUM(u.likes) as likesCount
    FROM users u 
    GROUP BY recommendedByUserId
) recomm on recomm.rid = u.id
ORDER BY recomm.recommCount DESC

现在我还需要计算一个用户拥有多少个由另一个用户推荐的帖子，并将其汇总到推荐器上。我想我可以这样做:

SELECT u.username, recomm.recommCount, recomm.likesCount, recomm.postsCount
FROM users u
INNER JOIN
(
    SELECT recommendedByUserId as rid, COUNT(*) as recommCount, SUM(u.likes) as likesCount, COUNT(posts.id) AS postsCount
    FROM users u 
    INNER JOIN posts ON u.id = posts.author_id
    GROUP BY recommendedByUserId
) recomm on recomm.rid = u.id

ORDER BY recomm.recommCount DESC

但这会产生奇怪的结果。

感谢您的任何意见!

Answer 1

这可能就是您想要的:

SELECT u.username, p.postsCount, recomm.recommCount, recomm.likesCount
FROM users u 
JOIN
 (
   SELECT author_id, COUNT(*) AS postsCount
   GROUP BY author_id
 )  AS p
ON u.id = p.author_id
JOIN
 (
   SELECT recommendedByUserId as rid, COUNT(*) as recommCount, SUM(u.likes) as likesCount
   FROM users u 
   GROUP BY recommendedByUserId
 ) recomm ON recomm.rid = u.id
ORDER BY recomm.recommCount DESC