php - 多对多关系连接三个表，对第三个表的结果进行限制 mysql 中第三个表的限制

Question

我有三个处于多对多关系的表。 1.播放列表 2.轨道 3.playlist_tracks

我想检索 10 个播放列表，最多 5 首歌曲。我该怎么做？ 我已经尝试过这种方式..

select t1.id as playlistId, t2.playlist_id as pivot_playlist_id, t2.track_id as track_id 
from playlist t1 
join playlist_tracks t2 on t1.id = t2.playlist_id
left join (
    select t3.id as track_id , t3.is_published 
    from tracks t3
    where t3.is_published = 1 
    group by t3.id limit 5
    ) xx on t2.track_id = xx.track_id 
where t1.prior != 0 AND t1.is_published = 1 ;

但没有得到正确的结果，因为它没有对轨道应用限制。它返回特定播放列表的所有歌曲。我做错的地方>请帮助我。这是相同的 DBfiddle sqlfiddle.com/#!9/feddbd/1

Answer 1

尝试将每个 playlist_track 限制为 5 首歌曲:

SET @playlist_id=-1;
SELECT * FROM
(
  SELECT track_id,
@row_number:=CASE
    WHEN @playlist_id= playlist_id THEN @row_number + 1
    ELSE 1
END AS track_number,
@playlist_id:=playlist_id as playlist_id
FROM playlist_tracks
ORDER BY playlist_id
) X WHERE track_number<=5