mysql 左连接和内连接 3 个表

Question

我有 3 个表：oc_artists、oc_songs、oc_songs_tags

我可以 select 2 个表使用此代码：

SELECT * FROM `oc_songs` LEFT JOIN oc_songs_tags ON oc_songs.song_id=oc_songs_tags.song_id 
WHERE oc_songs_tags.song_tag IS NULL

现在我需要 select 来自 oc_artists 的数据...我试过这个问题的答案： MySQL LEFT JOIN 3 tables

这是我的代码：

SELECT * FROM oc_songs
LEFT JOIN oc_artists
    INNER JOIN oc_songs_tags
    ON oc_songs.song_artist_id = oc_artists.artist_id
ON oc_songs_tags.song_id = oc_songs.song_id

但是我收到这个错误

8 errors were found during analysis.

Unrecognized keyword. (near "ON" at position 131)
Unexpected token. (near "oc_songs_tags" at position 134)
Unexpected token. (near "." at position 147)
Unexpected token. (near "song_id" at position 148)
Unexpected token. (near "=" at position 156)
Unexpected token. (near "oc_songs" at position 158)
Unexpected token. (near "." at position 166)
Unexpected token. (near "song_id" at position 167)

Answer 1

ON 子句位置错误

SELECT * FROM oc_songs
LEFT JOIN oc_artists ON oc_songs.song_artist_id = oc_artists.artist_id
INNER JOIN oc_songs_tags  ON oc_songs_tags.song_id = oc_songs.song_id

Answer 2

你的语法有误。加入语法是：

[JOIN TYPE] JOIN [TABLE B] ON [TABLE A].[COLUMN] = [TABLE B].[COLUMN]

所以这意味着：

SELECT * FROM oc_songs
 LEFT JOIN oc_artists ON oc_songs.song_artist_id = oc_artists.artist_id
 INNER JOIN oc_songs_tags ON oc_songs.song_id = oc_songs_tags.song_id

理解 JOINS 的简单方法是，它们始终是 FROM 中列出的主要 table 和您正在加入的 table 之间的连词。因此，将 JOIN 子句视为连词列表。

因此，要将 TableA 与 TableB、TableC 和 TableD 连接起来，您可能需要：

SELECT * FROM TableA
  JOIN TableB on TableA.tableb_id = TableB.id  -- this is first join
  JOIN TableC on TableA.tablec_id = TableC.id  -- this is second join
  JOIN TableD on TableA.tabled_id = TableD.id  -- this is third join

Answer 3

示例表：

DROP TABLE IF EXISTS `oc_songs` ;
DROP TABLE IF EXISTS `oc_songs_tags` ;
DROP TABLE IF EXISTS `oc_artists` ;

CREATE TABLE `oc_songs` (
  `song_id` int(10) unsigned NOT NULL auto_increment,
  `song_name` varchar(255) NOT NULL,
  `song_artist_id`  int(10),
  PRIMARY KEY  (`song_id`),
  foreign key (`song_artist_id`) references oc_artists(`artist_id`)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

CREATE TABLE `oc_songs_tags` (
  `song_tag_id` int(10) unsigned NOT NULL auto_increment,
  `song_tag` varchar(255) NOT NULL,
  `song_id` int(10),
  PRIMARY KEY  (`song_tag_id`),
  foreign key (`song_id`) references oc_songs(`song_id`)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

CREATE TABLE `oc_artists` (
  `artist_id` int(10) unsigned NOT NULL auto_increment,
  `artist_age` int(4),
  PRIMARY KEY  (`artist_id`)

) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

右select:

SELECT * FROM oc_songs
 LEFT JOIN oc_artists ON 
    oc_songs.song_artist_id = oc_artists.artist_id
 INNER JOIN oc_songs_tags ON 
    oc_songs.song_id = oc_songs_tags.song_id;

mysql 左连接和内连接 3 个表

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