php - 在不同表中查询 MySQL - 检索音乐播放列表

Question

我有三个表，第一个存储歌曲数据，第二个存储包含播放列表名称和所有者 ID 的播放列表，第三个表将歌曲 ID 链接到它们所属的播放列表。

问题是如何检索用户的播放列表及其包含的歌曲，同时限制对服务器的请求数量，有没有办法在单个查询中检索这些信息？

到目前为止，我拥有的 PHP 代码位于我的帖子的末尾。

任何帮助或建议都会很棒，我真的对此感到疯狂:)

谢谢

表1 song_main

   ID          song_artist          song_album            song_url           
   1             woops                 foo1                 www.                
   2              bob                  foo2                 www.                 

表 2 播放列表

  ID             title              owner_id               
   1           myplaylist               20                             
   1          myplaylist1               23                        

表 3 song_in_list

   ID           song_id            playlist_id               
   1               1                   20                             
   1               1                   23 

这是我的 php 代码，我基本上想先获取播放列表 id 和名称，然后运行第二个查询来获取每个播放列表包含的歌曲 id，然后运行第三个查询来获取每首歌曲信息。我只是不知道我所做的是否正确......

 //Getting user's playlists 
    $raw_resultsplaylists = mysql_query("SELECT * FROM playlists
    WHERE (`owner_id` = '$userid')" ) or die(mysql_error());

    //fetch the query and adding them to vars               
    $counter = 1;
    while($resultsplaylists = mysql_fetch_array($raw_resultsplaylists))
              {         
    ${"playlistname" . $counter} = $resultsplaylists['id'];
    ${"playlistid" . $counter} = $resultsplaylists['playlistid'];
    $counter= $counter+1;
            }

Answer 1

我创建了这些表:

CREATE TABLE IF NOT EXISTS `song_main` (
  `ID`              varchar(255),
  `song_artist`     varchar(255),
  `song_album`      varchar(255),
  `song_url`        varchar(255),
  PRIMARY KEY (`ID`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `song_in_list` (
  `ID`              varchar(255),
  `song_id`         varchar(255),
  `playlist_id`     varchar(255),
  PRIMARY KEY (`ID`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `playlists` (
  `ID`              varchar(255),
  `title`           varchar(255),
  `owner_id`        varchar(255),
  PRIMARY KEY (`ID`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;

插入此数据:

INSERT INTO `song_main` (`ID`, `song_artist`, `song_album`, `song_url`) VALUES
(1, 'Artist 1', 'Album 1', 'www.url1.com'),
(2, 'Artist 2', 'Album 2', 'www.url2.com'),
(3, 'Artist 3', 'Album 3', 'www.url3.com'),
(4, 'Artist 4', 'Album 4', 'www.url4.com');

INSERT INTO `song_in_list` (`ID`, `song_id`, `playlist_id`) VALUES
(1, 1, 1),
(2, 2, 1),
(3, 3, 1),
(4, 2, 2),
(5, 4, 2),
(6, 4, 3);

INSERT INTO `playlists` (`ID`, `title`, `owner_id`) VALUES
(1, 'Playlist 1 for owner 1', 1),
(2, 'Playlist 2 for owner 1', 1),
(3, 'Playlist 1 for owner 2', 2);

然后我可以使用此查询从用户 ID 1 获取所有播放列表中的所有歌曲:

SELECT songs.*, playlists.title as `playlist_title`
FROM song_main AS songs
JOIN song_in_list AS playlist_songs 
    ON songs.ID = playlist_songs.song_id
JOIN playlists 
    ON playlist_songs.playlist_id = playlists.ID
WHERE playlists.owner_id = 1

结果是:

ID  song_artist song_album  song_url    playlist_title
1   Artist 1    Album 1 www.url1.com    Playlist 1 for owner 1
2   Artist 2    Album 2 www.url2.com    Playlist 1 for owner 1
3   Artist 3    Album 3 www.url3.com    Playlist 1 for owner 1
2   Artist 2    Album 2 www.url2.com    Playlist 2 for owner 1
4   Artist 4    Album 4 www.url4.com    Playlist 2 for owner 1

您也可以轻松添加播放列表 ID:

SELECT songs.*, playlists.title as `playlist_title`
FROM song_main AS songs
JOIN song_in_list AS playlist_songs 
    ON songs.ID = playlist_songs.song_id
JOIN playlists 
    ON playlist_songs.playlist_id = playlists.ID
WHERE playlists.owner_id = 1
AND playlists.ID = 1