mysql加入限制1 [英] mysql join with limit 1

问题描述

假设我有两个表一对多.

Suppose I have two tables in one to many relationship.

而且，我想从每个主记录中选择列，并从相关表中选择第一条记录.

And, I want to select columns from each main record along with the first record from a related table.

我尝试了一些方法，但是没有成功...

I tried some ways but it just doesn't go...

在这里，我得到了这个SQL提琴:

Here I end up with this SQL fiddle:

http://sqlfiddle.com/#!2/39fdb/3

那里的问题是它不能从子选择中引用a.ID.

The problem there is that it just cannot reference a.ID from a subselect.

这当然不起作用，但这只是我能想到的

This does not work, of course, but it's just all I could think of

select a.*,b.* from event a left join 
(select * from event_pictures where a.ID=article limit 1)
b on a.ID=b.article;

关于如何解决它的任何想法?

Any ideas on how to fix it?

推荐答案

不，您不能在与a相连的子选择中引用a.ID.您可以执行以下操作，但是最好提供一个订购单.否则，将没有第一"行.将选择表b中的(或多或少)随机行:

No, you can't reference a.ID in a subselect that is joined to a. You can do the following, but you better supply an ordering. Otherwise, there is no "first" row. A (more or less) random row from table b will be selected:

select a.*, b.* 
from event a 
  left join event_pictures b
    on b.PK =                        --- the PRIMARY KEY
       ( select bb.PK                --- of event_pictures 
         from event_pictures bb 
         where a.ID = bb.article
         ORDER BY bb.something 
         limit 1
       ) ;

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