SQL将JOIN留下4列

Question

我有两张桌子

IDartist     name
----------- -----------
1           akon
2           50 cent

IDsong    name   IDartist   IDauthor   IDcomposer   IDmusicProducer
------    ----   --------   --------   ---------    ---------------
1         lonley    1         2           1              2

我是如何知道哪位艺术家，IS作者，IDcomposer，IDmusicProducer？

我试图这样做而且不起作用：

SELECT
songs.`IDsong`,
songs.`IDartist`,
songs.`name`,
songs.`IDgenre`,
songs.`IDauthor`,
songs.`IDcomposer`,
songs.`IDmusicProducer`,
artists.`name` As artists_name,
songs_genres.`name` As genres_name
FROM `songs`
LEFT OUTER JOIN `artists` ON (songs.`IDartist` = artists.`IDartist` OR songs.`IDauthor` = artists.`IDartist` OR songs.`IDcomposer` = artists.`IDartist` OR songs.`IDmusicProducer` = artists.`IDartist`)
LEFT OUTER JOIN `songs_genres` ON (songs.`IDgenre` = songs_genres.`IDgenre`)
WHERE songs.`IDsong`=XXX

Answer 1

为了获取艺术家，作者，作曲家和制作人的名字，您必须将artists表加入songs表中不同的时间。查询应如下所示：

SELECT
s.IDsong, s.name,
a1.name AS artists_name,
a2.name AS author_name,
a3.name AS composer_name,
a4.name AS producer_name,
sg.name AS genres_name
FROM songs AS s
  JOIN artists AS a1 ON s.IDartist = a1.IDartist
  JOIN artists AS a2 ON s.IDauthor = a2.IDartist
  JOIN artists AS a3 ON s.IDcomposer = a3.IDartist
  JOIN artists AS a4 ON s.IDmusicProducer = a4.IDartist
  JOIN songs_genres AS sg ON s.IDgenre = sg.IDgenre

如果某位唱片可能没有艺术家，作家，作曲家和制作人，那么您将不得不在表格上使用LEFT JOIN。