每次2张桌子上的UNION每次都会返回一个几乎为空的结果

Question

我有一个叫做Galleries的东西，将媒体组合在一起。 该媒体可以是照片或视频。 我将照片存储在一个表中，将视频存储在另一个表中，所以我使用UNION查询来查找属于图库的照片和视频。

我的问题似乎是我的结果包含其中一个表的空对象（无ID），换句话说，如果该表中没有结果，它将始终为被查询的表之一返回无用的结果。

一，查询：

SELECT * from (
    SELECT g.id AS gallery_id,  'photo' AS type, p.id AS id, p.filename, p.caption, null AS title, null AS service, null AS embed, null AS width, null AS height, p.display_order FROM galleries g 
        LEFT OUTER JOIN photos AS p ON p.gallery_id = g.id
        WHERE g.id = {$this->id}
    UNION
    SELECT g.id AS gallery_id, 'video' AS type, v.id AS id, null AS filename, null AS caption, v.title, v.service, v.embed, v.width, v.height, v.display_order FROM galleries g 
        LEFT OUTER JOIN videos AS v ON v.gallery_id = g.id 
        WHERE g.id = {$this->id}
) AS u ORDER BY display_order;

我正在添加type列，以便可以确定返回哪种结果。 我已经清空了表之间不常见的结果。

就像我说的那样，它可以工作，但并不完全符合预期。 如果我的画廊只包含照片，我仍然会得到（几乎）空的视频结果。 结果示例：

[] => Galleries Object
    (
        [id] => 
        [name] => 
        [slug] => 
        [gallery_id] => 32
        [type] => video
        [filename] => 
        [caption] => 
        [title] => 
        [service] => 
        [embed] => 
        [width] => 
        [height] => 
        [display_order] => 
    )

[39] => Galleries Object
    (
        [id] => 39
        [name] => 
        [slug] => 
        [gallery_id] => 32
        [type] => photo
        [filename] => 39-studio-blue-pacific.jpg
        [caption] => 
        [title] => 
        [service] => 
        [embed] => 
        [width] => 
        [height] => 
        [display_order] => 1
    )

标记为[type]=>video的第一个结果为空，我称之为它，因为它没有视频ID，标题，嵌入代码等。它仅包含gallery_id和type 。

这是迄今为止我提出的最复杂的查询，并且我肯定有一些遗漏之处。 如果图库仅包含视频或仅包含照片，我希望结果能反映出来。

作为黑客，我可以在回显某些内容之前检查这些结果时是否查看ID ，但我知道可以改进查询。 救命？

Answer 1

之所以返回这些结果，是因为您在表上使用了外部联接。 尝试以下方法：

SELECT * from (
    SELECT g.id AS gallery_id,  'photo' AS type, p.id AS id, p.filename, p.caption, null AS title, null AS service, null AS embed, null AS width, null AS height, p.display_order FROM galleries g 
        JOIN photos AS p ON p.gallery_id = g.id
        WHERE g.id = {$this->id}
    UNION
    SELECT g.id AS gallery_id, 'video' AS type, v.id AS id, null AS filename, null AS caption, v.title, v.service, v.embed, v.width, v.height, v.display_order FROM galleries g 
        JOIN videos AS v ON v.gallery_id = g.id 
        WHERE g.id = {$this->id}
) AS u ORDER BY display_order;

同样，听起来您从阅读我撰写的有关SQL的文章中可能会受益匪浅，以帮助您更好地理解这些概念。