Question

这是我的问题：我有4个表来保存用户完成的帖子（比如CatA，CatB，CatC和CatD，每个表保持created_by列）。我的要求是从表USER获取所有用户的帖子数（帖子总和）。

我很难找到过去2天的答案，我仍然无能为力。

非常感谢任何想法。

SELECT    u.username,
          a.cnt + b.cnt + c.cnt + d.cnt AS total_posts
FROM      users u
LEFT JOIN (SELECT created_by, COUNT(*) AS cnt FROM CatA GROUP BY created_by) a
          ON u.id = a.created_by
LEFT JOIN (SELECT created_by, COUNT(*) AS cnt FROM CatB GROUP BY created_by) b
          ON u.id = b.created_by
LEFT JOIN (SELECT created_by, COUNT(*) AS cnt FROM CatC GROUP BY created_by) c
          ON u.id = c.created_by
LEFT JOIN (SELECT created_by, COUNT(*) AS cnt FROM CatD GROUP BY created_by) d
          ON u.id = d.created_by
ORDER BY total_posts DESC

这会将我的总帖子数量排在最前面（不论用户帖子数量如下），而不是每个用户的帖子数

用户名| user1 | user2 |用户3
total_posts | 11020（总帖数）| NULL | NULL |等等

更多信息：

SELECT created_by, COUNT(*) AS cnt FROM CatA GROUP BY created_by

这让我回报：

created_by | 22 | 26 | 88 | 90个
cnt | 6 | 20 | 15 | 8

Answer 1

所以看起来每个类别都有一个单独的表（顺便说一下，它实际上不是最优化的设计）。您可以采取哪些措施来获取所有用户的帖子数量：

SELECT    u.*,
          a.cnt + b.cnt + c.cnt + d.cnt AS total_posts
FROM      users u
LEFT JOIN (SELECT user_id, COUNT(*) AS cnt FROM CatA GROUP BY user_id) a
          ON u.user_id = a.user_id
LEFT JOIN (SELECT user_id, COUNT(*) AS cnt FROM CatB GROUP BY user_id) b
          ON u.user_id = b.user_id
LEFT JOIN (SELECT user_id, COUNT(*) AS cnt FROM CatC GROUP BY user_id) c
          ON u.user_id = c.user_id
LEFT JOIN (SELECT user_id, COUNT(*) AS cnt FROM CatD GROUP BY user_id) d
          ON u.user_id = d.user_id

如何获取用户完成的帖子数量

1 个答案: