MySQL 在同一个表上有 2 个 LEFT JOIN

发布于 2024-07-21 20:48:59 字数 1760 浏览 4 评论 0原文

我正在尝试运行此查询：

SELECT 
  Destaque.destaque, Noticia.id, Noticia.antetitulo, 
  Noticia.titulo, Noticia.lead, Noticia.legenda, 
  Noticia.publicacao, Seccao.descricao, Album.pasta,
  Foto.ficheiro, Foto.descricao, Cronista.nome, 
  Cronista.profissao, Cronista.ficheiro,
  AudioFile.*, AudioCollection.*, VideoFile.*, VideoCollection.*
FROM 
  nt_highlights AS Destaque
  LEFT JOIN nt_noticias  AS Noticia         ON Destaque.noticia_id = Noticia.id
  LEFT JOIN mm_fotos     AS Foto            ON Noticia.foto_id = Foto.id
  LEFT JOIN nt_temas     AS Seccao          ON Noticia.tema_id = Seccao.id
  LEFT JOIN mm_albuns    AS Album           ON Foto.album_id = Album.id
  LEFT JOIN nt_cronistas AS Cronista        ON Cronista.id = Noticia.cronista_id  
  LEFT JOIN ntNoticias_mmFiles AS Rel       ON Rel.noticia_id = Noticia.id
  LEFT JOIN mm_files     AS AudioFile       ON AudioFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS AudioCollection ON AudioFile.coleccao_id = AudioCollection.id        
  LEFT JOIN mm_files     AS VideoFile       ON VideoFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS VideoCollection ON VideoFile.coleccao_id = VideoCollection.id
WHERE 
  Destaque.area_id = 1
  AND Noticia.paraPublicacao = 1 
  AND Noticia.publicacao <= NOW()   
  AND (AudioFile.mimeType != '' OR AudioFile.id IS NULL)
  AND (VideoFile.mimeType = '' OR VideoFile.id IS NULL)
ORDER BY 
  Destaque.destaque

这将为我提供一些文章（来自 nt_noticias），其想法是同时获取 Video 和 < mm_files 表中的 code>Audio 文件。

发生的情况是，当我有一篇带有声音和视频的文章时，MySQL 将返回 4 行：

带有声音（视频为空）
带有视频（声音为空）
带有所有空值
带有声音和视频

我怎样才能“强制”它在每篇文章中只返回一行与任何现有的视频和音频相关的内容？我在这里做错了什么？

原文

I'm trying to run this query:

SELECT 
  Destaque.destaque, Noticia.id, Noticia.antetitulo, 
  Noticia.titulo, Noticia.lead, Noticia.legenda, 
  Noticia.publicacao, Seccao.descricao, Album.pasta,
  Foto.ficheiro, Foto.descricao, Cronista.nome, 
  Cronista.profissao, Cronista.ficheiro,
  AudioFile.*, AudioCollection.*, VideoFile.*, VideoCollection.*
FROM 
  nt_highlights AS Destaque
  LEFT JOIN nt_noticias  AS Noticia         ON Destaque.noticia_id = Noticia.id
  LEFT JOIN mm_fotos     AS Foto            ON Noticia.foto_id = Foto.id
  LEFT JOIN nt_temas     AS Seccao          ON Noticia.tema_id = Seccao.id
  LEFT JOIN mm_albuns    AS Album           ON Foto.album_id = Album.id
  LEFT JOIN nt_cronistas AS Cronista        ON Cronista.id = Noticia.cronista_id  
  LEFT JOIN ntNoticias_mmFiles AS Rel       ON Rel.noticia_id = Noticia.id
  LEFT JOIN mm_files     AS AudioFile       ON AudioFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS AudioCollection ON AudioFile.coleccao_id = AudioCollection.id        
  LEFT JOIN mm_files     AS VideoFile       ON VideoFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS VideoCollection ON VideoFile.coleccao_id = VideoCollection.id
WHERE 
  Destaque.area_id = 1
  AND Noticia.paraPublicacao = 1 
  AND Noticia.publicacao <= NOW()   
  AND (AudioFile.mimeType != '' OR AudioFile.id IS NULL)
  AND (VideoFile.mimeType = '' OR VideoFile.id IS NULL)
ORDER BY 
  Destaque.destaque

This will get me a number of articles (from nt_noticias) and the idea is to get at the same time a Video and an Audio file from the mm_files table.

What happens is that when I have an article with a sound and a video, MySQL will return 4 rows:

with the sound (video is null)
with the video (sound is null)
with all nulls
with the sound AND the video

How can I "force" it to return just one row per article with any existing video AND audio associated? What am I doing wrong here?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

从此见与不见 2024-07-28 20:48:59

我认为您想要这样的东西：

SELECT 
  Destaque.destaque, Noticia.id, Noticia.antetitulo, 
  Noticia.titulo, Noticia.lead, Noticia.legenda, 
  Noticia.publicacao, Seccao.descricao, Album.pasta,
  Foto.ficheiro, Foto.descricao, Cronista.nome, 
  Cronista.profissao, Cronista.ficheiro,
  AudioFile.*, AudioCollection.*, VideoFile.*, VideoCollection.*
FROM 
  nt_highlights AS Destaque
  LEFT JOIN nt_noticias  AS Noticia         ON Destaque.noticia_id = Noticia.id
  LEFT JOIN mm_fotos     AS Foto            ON Noticia.foto_id = Foto.id
  LEFT JOIN nt_temas     AS Seccao          ON Noticia.tema_id = Seccao.id
  LEFT JOIN mm_albuns    AS Album           ON Foto.album_id = Album.id
  LEFT JOIN nt_cronistas AS Cronista        ON Cronista.id = Noticia.cronista_id  
  LEFT JOIN ntNoticias_mmFiles AS AudioRel  ON Rel.noticia_id = Noticia.id
                                               AND AudioRel.file_id IN (
    SELECT file_id 
    FROM   ntNoticias_mmFiles 
    WHERE  noticia_id = Noticia.id AND IsAudioFile = 1 /* whatever the check is */
    LIMIT  1
  )
  LEFT JOIN mm_files     AS AudioFile       ON AudioFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS AudioCollection ON AudioFile.coleccao_id = AudioCollection.id        
  LEFT JOIN ntNoticias_mmFiles AS VideoRel  ON VideoRel.noticia_id = Noticia.id
                                               AND VideoRel.file_id IN (
    SELECT file_id 
    FROM   ntNoticias_mmFiles 
    WHERE  noticia_id = Noticia.id AND IsVideoFile = 1  /* whatever the check is */
    LIMIT  1
  )
  LEFT JOIN mm_files     AS VideoFile       ON VideoFile.id = Rel.file_id
                                               AND VideoFile.IsVideoFile = 1
  LEFT JOIN mm_coleccoes AS VideoCollection ON VideoFile.coleccao_id = VideoCollection.id
WHERE 
  Destaque.area_id = 1
  AND Noticia.paraPublicacao = 1 
  AND Noticia.publicacao <= NOW()   
ORDER BY 
  Destaque.destaque

我的想法是这样的：

您最多需要一个音频文件和一个视频文件。每个 Noticia 有多个可用文件，因此您需要确保每种类型最多有一个文件进入连接。这也意味着您必须加入 ntNoticias_mmFiles 表两次 - 每种类型一次。

这就是连接条件中的子查询应该执行的操作：每种文件类型选择一行。从那里继续，您将其余数据保留在其中，就像您已经做的那样。

I think you want something like this:

SELECT 
  Destaque.destaque, Noticia.id, Noticia.antetitulo, 
  Noticia.titulo, Noticia.lead, Noticia.legenda, 
  Noticia.publicacao, Seccao.descricao, Album.pasta,
  Foto.ficheiro, Foto.descricao, Cronista.nome, 
  Cronista.profissao, Cronista.ficheiro,
  AudioFile.*, AudioCollection.*, VideoFile.*, VideoCollection.*
FROM 
  nt_highlights AS Destaque
  LEFT JOIN nt_noticias  AS Noticia         ON Destaque.noticia_id = Noticia.id
  LEFT JOIN mm_fotos     AS Foto            ON Noticia.foto_id = Foto.id
  LEFT JOIN nt_temas     AS Seccao          ON Noticia.tema_id = Seccao.id
  LEFT JOIN mm_albuns    AS Album           ON Foto.album_id = Album.id
  LEFT JOIN nt_cronistas AS Cronista        ON Cronista.id = Noticia.cronista_id  
  LEFT JOIN ntNoticias_mmFiles AS AudioRel  ON Rel.noticia_id = Noticia.id
                                               AND AudioRel.file_id IN (
    SELECT file_id 
    FROM   ntNoticias_mmFiles 
    WHERE  noticia_id = Noticia.id AND IsAudioFile = 1 /* whatever the check is */
    LIMIT  1
  )
  LEFT JOIN mm_files     AS AudioFile       ON AudioFile.id = Rel.file_id
  LEFT JOIN mm_coleccoes AS AudioCollection ON AudioFile.coleccao_id = AudioCollection.id        
  LEFT JOIN ntNoticias_mmFiles AS VideoRel  ON VideoRel.noticia_id = Noticia.id
                                               AND VideoRel.file_id IN (
    SELECT file_id 
    FROM   ntNoticias_mmFiles 
    WHERE  noticia_id = Noticia.id AND IsVideoFile = 1  /* whatever the check is */
    LIMIT  1
  )
  LEFT JOIN mm_files     AS VideoFile       ON VideoFile.id = Rel.file_id
                                               AND VideoFile.IsVideoFile = 1
  LEFT JOIN mm_coleccoes AS VideoCollection ON VideoFile.coleccao_id = VideoCollection.id
WHERE 
  Destaque.area_id = 1
  AND Noticia.paraPublicacao = 1 
  AND Noticia.publicacao <= NOW()   
ORDER BY 
  Destaque.destaque

My thought was this:

You want one audio file and one video file, at most. There are several files available per Noticia, so you need to make sure that a maximum of one file per type gets into the join. This also means you have to join in the ntNoticias_mmFiles table twice — once per type.

This is what the sub-queries in the join conditions are supposed to do: Select one row per file type. Going on from there you LEFT JOIN the rest of the data in, just like you already do.

回复收藏 0 原文

我三岁 2024-07-28 20:48:59

JOIN 将返回所有组合，这就是问题所在。
如果每篇文章只有一个音频和/或视频文件，那么您可能需要查看子选择。
在 SQL Server 中，这看起来像（未经测试的代码）：

SELECT title, 
       (select TOP 1 audio from audio where audio.aid = articles.id) as Audio, 
       (select TOP 1 video from video where video.aid = articles.id) as Video
FROM articles

请注意，在大型数据集上，这可能会表现不佳，因为此示例中的子选择是针对返回到外部查询的每一行单独执行的。例如，如果您返回 10,000 篇文章，那么服务器上实际上将执行总共 20,001 个查询。
还有其他可能的答案来克服这个问题，但它们涉及更多（我怀疑您可以使用派生表做一些事情，但目前我无法做到）。

The JOIN will return all the combinations, that's the problem.
If you only have one audio and/or videofile per article then you might want to look at subselects.
In SQL Server this would look something like (untested code):

SELECT title, 
       (select TOP 1 audio from audio where audio.aid = articles.id) as Audio, 
       (select TOP 1 video from video where video.aid = articles.id) as Video
FROM articles

Be careful that on large datasets this can perform poorly as the subselects in this example are executed individually for each row returned to the outer query. For example, if you return 10,000 articles then a total of 20,001 queries would actually be executed on the server.
There are other possible answers to overcome this but they get more involved (I suspect you could do something with a derived table but it eludes me at the moment).

回复收藏 0 原文