MySQL按2行的计算值排序

Question

我正在尝试创建一个 MySQL 语句，该语句将按语句本身计算的值进行排序。我的表格如下所示:

posts
+----+-----------+--------------+
| ID | post_type | post_content |
+----+-----------+--------------+
|  1 |      post |        Hello |
|  2 |      post |        world |
+----+-----------+--------------+

postmeta
+---------+----------+------------+
| post_id | meta_key | meta_value |
+---------+----------+------------+
|       1 |    price |         50 |
|       1 |   retail |        100 |
|       2 |    price |         60 |
|       2 |   retail |         90 |
+---------+----------+------------+

我正在尝试计算一个称为储蓄的值(ID=1 为 .5，ID= 为 .3 2) 然后按它排序。这是我到目前为止所拥有的，但我不确定如何跨两行进行计算(我发现的所有内容都是关于列之间的计算)。

SELECT wposts.*
FROM $wpdb->posts wposts, $wpdb->postmeta wpostmeta
WHERE wposts.ID = wpostmeta.post_id
AND wpostmeta.meta_key = 'Price'
AND wposts.post_type = 'post'
ORDER BY wpostmeta.meta_value DESC

感谢您的帮助!

Answer 1

这是一个简单的连接，它将计算每个帖子的节省量，假设 meta_value 是数字数据类型。

select posts.id,
       (retail.meta_value - price.meta_value) * 1.0 / retail.meta_value as savings
  from posts,
       (select * from postmeta where meta_key = 'price') as price,
       (select * from postmeta where meta_key = 'retail') as retail
 where posts.id = price.post_id
   and posts.id = retail.post_id
   and posts.post_type = 'post'
 order by savings;


+----+---------+
| id | savings |
+----+---------+
|  1 | 0.50000 |
|  2 | 0.33333 |
+----+---------+