连接多个表的计数

Question

am building a blog for music and i want to count the number of likes and comments each blog post has when listing all the blog post. i have the tables needed . this is my query

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  

what i noticed is that it multiplies the count of comments with the count of likes and supplies the answer as the count of likes ie (if a post has 4 comments and 1 like, my query will display 4 comments and 4 likes) this has been really frustrating

Answer 1

The problem is you have two different dimensions, so the query is producing a Cartesian product for each music id.

The best solution is to aggregate before joining:

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 ;