mysql - 为什么 mysql 查询多个计数语句返回单个值？

Question

我正在创建简单的图库，每个图库都可以是混合图像/视频。在画廊列表中，我想显示每个画廊的图像/视频数量。但是，我只收到一个结果行，真的不知道为什么。

画廊表示例:

id  title
=====================
1   Simple gallery
2   Test gallery

简单的 gallery_items 表:

id  gallery_id  type   title
================================
1   1           image  title1
2   1           image  title2
3   1           video  title3
4   1           image  title4
5   2           image  title5
6   2           image  title6

我正在使用的查询是:

select galleries.*, count(distinct A.id) as IMG, count(distinct B.id) as VID 
from galleries
left join gallery_items A on (galleries.id=A.gallery_id and A.type='image')
left join gallery_items B on (galleries.id=B.gallery_id and B.type='video')

这产生了预期的结果:

id  title           IMG VID
================================
1   Simple gallery  3   1

但问题是只显示一行。无法显示所有行...有什么想法吗？

Answer 1

是的，Salmon 是对的...只需添加“group by galleries.id”即可解决问题:)

select galleries.*, count(distinct A.id) as IMG, count(distinct B.id) as VID 
from galleries
left join gallery_items A on (galleries.id=A.gallery_id and A.type='image')
left join gallery_items B on (galleries.id=B.gallery_id and B.type='video')
group by galleries.id