mysql - 连接多个表的计数

Question

我正在建立一个音乐博客，我想在列出所有博客文章时计算每个博客文章的喜欢和评论数量。我有需要的 table 。这是我的查询

SELECT tbl_music.id,
                               tbl_music.name,
                               tbl_music.img,
                               tbl_music.date,
                               tbl_music.post,
                               COUNT(*) AS comms,
                               COUNT(*) AS liky

                        FROM tbl_music 

                        LEFT JOIN tbl_mlikes
                        ON tbl_music.id = tbl_mlikes.mid
                        LEFT JOIN tbl_mus_coms
                        ON tbl_music.id = tbl_mus_coms.mid
                        WHERE tbl_music.status = 'Publish' 
                        GROUP BY tbl_music.id
                        ORDER BY tbl_music.id 
                        DESC  

我注意到，它将评论数与喜欢数相乘，并提供答案作为喜欢数，即(如果帖子有 4 条评论和 1 条喜欢，我的查询将显示 4 条评论和 4 条喜欢)这真的很令人沮丧

Answer 1

问题是您有两个不同的维度，因此查询会为每个音乐 id 生成笛卡尔积。

最好的解决方案是在加入之前聚合:

SELECT m.*, l.likes, c.comments
FROM tbl_music m LEFT JOIN
     (SELECT mid, COUNT(*) as likes
      FROM tbl_mlikes
      GROUP BY mid
     ) l
     ON m.id = l.mid LEFT JOIN
     (SELECT mc.mid, COUNT(*) as comments
      FROM tbl_mus_coms mc
      GROUP BY mc.mid
     ) c
     ON m.id = c.mid
WHERE m.status = 'Publish' 
ORDER BY m.id DESC ;