按具有多对多关系的连接字段排序

Question

在 PostgreSQL 数据库中，有两个实体具有多对多关系：songs 具有多对多 artists。 artists_songs 表用于关系。我想选择歌曲并按第一位艺术家对它们进行排序（按字母顺序排序）。目前 PG 不允许我在不指定 group by 的所有字段的情况下这样做。是否可以仅按songs.id 分组选择和排序歌曲？

这是我的 SQL 查询：

select ss.*
  from (
    select songs.*, min(artists.name) as artist_name
    from songs
      left join artists_songs on artists_songs.song_id = songs.id
      left join artists on artists.id = artists_songs.artist_id
      group by songs.id, artists.name
    ) ss
    group by ss.id
    order by ss.artist_name
    ;

Answer 1

这看起来是横向连接的好地方：

select s.*, a.name
from songs s
cross join lateral (
    select a.name
    from artists_songs ars
    inner join artists a on a.id = ars.artist_id
    where ars.song_id = s.id
    order by a.name
    limit 1
) a
order by a.name

Answer 2

使用distinct on:

select distinct on (s.id) s.*, sa.name as artist_name
from songs s left join
     artists_songs ars
     on ars.song_id = s.id left join
     artists a
     on a.id = ars.artist_id    
order by s.id, sa.name;

如果你想要特定的排序，你可以使用子查询：

select s.*
from (select distinct on (s.id) s.*, sa.name as artist_name
      from songs s left join
           artists_songs ars
           on ars.song_id = s.id left join
           artists a
           on a.id = ars.artist_id    
      order by s.id, sa.name
     ) s
order by artist_name

Answer 3

到目前为止，我提出的最佳解决方案是使用 @gordon-linoff 最初所说的窗口函数：

select s.id, min(a.name) over (partition by s.id) as artist_name
from songs s left join
    artists_songs ars
    on ars.song_id = s.id left join
    artists a
    on a.id = ars.artist_id
order by artist_name;