LEFT JOIN 仅第一行

问题描述

我阅读了很多关于只获取左连接的第一行的帖子，但是由于某种原因，这对我不起作用.

I read many threads about getting only the first row of a left join, but, for some reason, this does not work for me.

这是我的结构(当然是简化的)

Here is my structure (simplified of course)

供稿

id |  title | content
----------------------
1  | Feed 1 | ...

艺术家

artist_id | artist_name
-----------------------
1         | Artist 1
2         | Artist 2

feeds_artists

rel_id | artist_id | feed_id
----------------------------
1      |     1     |    1 
2      |     2     |    1 
...

现在我想获取文章并且只加入第一个艺术家，我想到了这样的事情:

Now i want to get the articles and join only the first Artist and I thought of something like this:

SELECT *
    FROM feeds 
    LEFT JOIN feeds_artists ON wp_feeds.id = (
        SELECT feeds_artists.feed_id FROM feeds_artists
        WHERE feeds_artists.feed_id = feeds.id 
    LIMIT 1
    )
WHERE feeds.id = '13815'

只是为了只获取 feeds_artists 的第一行，但这已经不起作用了.

just to get only the first row of the feeds_artists, but already this does not work.

由于我的数据库，我无法使用 TOP 并且我无法按 feeds_artists.artist_id 对结果进行分组，因为我需要按日期对它们进行排序(我得到了结果通过这种方式对它们进行分组，但结果不是最新的)

I can not use TOP because of my database and I can't group the results by feeds_artists.artist_id as i need to sort them by date (I got results by grouping them this way, but the results where not the newest)

也用 OUTER APPLY 尝试了一些东西 - 也没有成功.老实说，我真的无法想象那些行中发生了什么 - 可能是我无法让它工作的最大原因.

Tried something with OUTER APPLY as well - no success as well. To be honest i can not really imagine whats going on in those rows - probably the biggest reason why i cant get this to work.

解决方案:

SELECT *
FROM feeds f
LEFT JOIN artists a ON a.artist_id = (
    SELECT artist_id
    FROM feeds_artists fa 
    WHERE fa.feed_id = f.id
    LIMIT 1
)
WHERE f.id = '13815'

推荐答案

@Matt Dodges 的回答让我走上了正轨.再次感谢所有的答案，同时帮助了很多人.让它像这样工作:

@Matt Dodges answer put me on the right track. Thanks again for all the answers, which helped a lot of guys in the mean time. Got it working like this:

SELECT *
FROM feeds f
LEFT JOIN artists a ON a.artist_id = (
    SELECT artist_id
    FROM feeds_artists fa 
    WHERE fa.feed_id = f.id
    LIMIT 1
)
WHERE f.id = '13815'

这篇关于LEFT JOIN 仅第一行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！