MySQL排序结果由两个关系计数的总和（*）

Question

我想按两个相关表条目的计数（*）对结果进行排序。

所以我想获得具有更多 cmets + 帖子交互的排名最高的用户 ID。

---

用户表：
ID Name @ 987654323@
1 Jonh
2 @ 987654327@
3 King
4 Doe kbd>

发布表：
ID USER_ID@ 987654334@
1 1
2 @ 987654338@
3 3
4 1 kbd>

评论表：
ID USER_ID@ 987654345@
1 1
2 @ 987654349@
3 1
4 4 kbd>

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按帖子数排序(*)：

SELECT user.*, COUNT(post.user_id) AS count FROM user
LEFT JOIN post ON user.id = post.user_id
GROUP BY user.id
ORDER BY count DESC

按评论数排序(*)

SELECT user.*, COUNT(comment.user_id) AS count FROM user
LEFT JOIN comment ON user.id = comment.user_id
GROUP BY user.id
ORDER BY count DESC

---

按帖子排序+评论计数（*）

预期结果： user_id：1（四次交互），3（两次交互），4（一次交互）

Answer 1

SELECT u.*, COUNT(interact.user_id)
FROM user u
LEFT JOIN  ( SELECT user_id  FROM post
             UNION ALL
             SELECT user_id  FROM comment 
           ) interact
 ON u.user_id = interact.user_id
GROUP BY u.user_id

如果你想要更多细节可以使用条件计数

SELECT u.*, 
       COUNT(CASE WHEN source = 'p' then 1 END) as total_p,
       COUNT(CASE WHEN source = 'c' then 1 END) as total_c,
       COUNT(interact.user_id) as total_interact
FROM user u
LEFT JOIN  ( SELECT user_id, 'p' as source  FROM post
             UNION ALL
             SELECT user_id, 'c' as source  FROM comment 
           ) interact
 ON u.user_id = interact.user_id
GROUP BY u.user_id