左联接将主键连接到普通列会造成严重破坏

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问题描述

下面的链接与我的问题有关

Link below is related to my question:

出色的左联接，得到意想不到的结果

这是我的表格结构，仅供参考.

Here's my table structure just to give an overview.

选项:

事件元:

嗯，这确实是同样的问题，但我认为是因为口才好.当我尝试使用PDO查询链接上的问题时.还是一样.

Well, it really is the same problem but I thought it's because of Eloquent. When I tried to use PDO querying the problem on my link. It still does the same.

$query = $db->prepare(
    "   SELECT      * FROM event_meta a
        LEFT JOIN   options b ON b.id = a.meta_value
        WHERE       a.meta_key = 'logo'
"); $query->execute();

$object = $query->fetchObject();

echo $object->value, '<br>';
echo $object->meta_value;

所以我要做的是，我有一个名为event_meta的表，并尝试连接options表以连接它们，我使用b.id，对于event_meta为a.meta_value

So what I did is, I have a table called event_meta and trying to join the options table to connect them I use b.id and for event_meta is a.meta_value

我最后要发生的事情是首先检索options.value以检查其是否为空.如果为空，我将得到event_meta.meta_value的值来输出它.

What I want to happen on my end is to retrieve the options.value first to check if it's empty. If it is empty, I will get the event_meta.meta_value's value to output it.

例如，在上面的查询中，我想获取称为徽标的meta_key.它应该获得图像名称的输出.但是，由于我已连接到options表，因此应该获取options.value.输出options.value时，应为空白.由于徽标的meta_value不等于任何options.id.但这是在检索Top Up值.

So for example on my query above, I want to get the meta_key called logo. It should get the output of an image name. But since I'm connected to options table it should get the options.value. When outputting the options.value it should be blank. Since the meta_value of logo does not equals to any options.id. But it's retrieving the Top Up value.

the

左联接将主键连接到普通列会造成严重破坏

问题描述

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