MYSQL根据特定列选择多个列

我想做一个SELECT请求,根据PLATFORM值,设法获得2列VALUE(DESKTOP& MOBILE).

这是一个示例表：

+----+---------+------+----------+-------+
| ID | PROJECT | NAME | PLATFORM | VALUE |
+----+---------+------+----------+-------+
|  1 |       1 | Foo  | desktop  |     1 |
|  2 |       1 | Foo  | mobile   |    42 |
|  3 |       1 | Bar  | desktop  |     3 |
|  4 |       1 | Bar  | mobile   |    10 |
|  5 |       2 | Foo  | desktop  |     2 |
|  6 |       2 | Bar  | mobile   |     9 |
+----+---------+------+----------+-------+

期望的输出：

+---------+------+---------+--------+
| PROJECT | NAME | DESKTOP | MOBILE |
+---------+------+---------+--------+
|       1 | Foo  | 1       | 42     |
|       1 | Bar  | 3       | 10     |
|       2 | Foo  | 2       | NULL   |
|       2 | Bar  | NULL    | 9      |
+---------+------+---------+--------+

我尝试了什么：

SELECT project,name,(CASE platform WHEN 'desktop' THEN value END) AS "desktop",(CASE platform WHEN 'mobile' THEN value END) AS "mobile"
FROM test
GROUP BY name,project
ORDER BY project,value ASC

+---------+------+---------+--------+
| project | name | desktop | mobile |
+---------+------+---------+--------+
|       1 | Foo  | 1       | NULL   |
|       1 | Bar  | 3       | NULL   |
|       2 | Foo  | 2       | NULL   |
|       2 | Bar  | NULL    | 9      |
+---------+------+---------+--------+

最佳答案

试试这个：

SELECT project,NAME,MAX(desktop) AS desktop,MAX(mobile) AS mobile FROM (
    SELECT project,(CASE platform WHEN 'desktop' THEN VALUE END) AS "desktop",(CASE platform WHEN 'mobile' THEN VALUE END) AS "mobile"
    FROM test
    ) AS aa
GROUP BY aa.NAME,aa.project
ORDER BY aa.project

说明：

首先,您可以选择(aa)所有数据,根据平台内容扩展价值.

然后使用该选择作为分组数据的原点.

结果：

project name   desktop mobile
1       Foo       1       42
1       Bar       3       10
2       Foo       2       NULL
2       Bar       NULL    9

原文地址：https://www.jb51.cc/mysql/432882.html