如何在每个音乐专辑中找到最短的歌曲名称

Question

我使用 mysql 并且我有两个具有多对多关系的表，第三个表包含它们的外键：

album table:
id  name   

composition table: 
id name duration

links table:
id  album_id    composition_id

如何创建 sql 查询以按时长获取每张专辑中最短的歌曲名称？ 我试图让一些想法像：

SELECT al.name, c.name FROM album al
JOIN links l ON l.album_id = al.id
JOIN composition c ON l.composition_id = c.id
GROUP BY al.name
HAVING //don't know what next

Answer 1

如果您使用 PostgreSQL：

SELECT DISTINCT ON (al.name) al.name, c.name FROM album al
JOIN links l ON l.album_id = al.id
JOIN composition c ON l.composition_id = c.id
ORDER BY al.name, c.duration

https://www.geekytidbits.com/postgres-distinct-on/

Answer 2

SELECT album_name, composition_name, duration
FROM (
  SELECT al.name AS album_name, 
    c.name AS composition_name,
    c.duration
    ROW_NUMBER() OVER (PARTITION BY al.id ORDER BY c.duration) AS rownum
  FROM album al
  JOIN links l ON l.album_id = al.id
  JOIN composition c ON l.composition_id = c.id
) AS t
WHERE rownum = 1;

Window 功能需要 MySQL 8.0。