mysql - 使用 SQL 查找所有轨道均由同一 Composer 创作的播放列表？

Question

我有三个表:

1. 播放列表(PlaylistId、名称)
2. PlaylistTrack(PlaylistId, TrackId)
3. 轨道(轨道 ID、名称、 Composer )

我必须找到所有轨道都由同一 Composer 创作的所有播放列表 ID？

我尝试了这个查询，但答案不正确:

SELECT P.PlaylistId
FROM PlatList P , PlaylistTrack PT
WHERE P.PlaylistId = PT.PlaylistID AND PT.TrackId = (SELECT T1.TrackId
                                                     FROM Track T1, Track T2
                                                     WHERE T1.Composer = T2.Composer)
GROUP BY P.PlaylistId

Answer 1

只需使用 HAVING 子句过滤每个包含多个 Composer 的播放列表即可。

SELECT
p.PlaylistId
FROM
Playlist p
JOIN PlaylistTrack pt ON p.PlaylistId = pt.PlaylistId
JOIN Track t ON pt.TrackId = t.TrackId
GROUP BY p.PlaylistId
HAVING COUNT(DISTINCT t.Composer) = 1;

并使用 JOIN 子句来连接表，而不是 WHERE 子句。