MYSQL根据特定列选择多个列

Question

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      |
+---------+------+---------+--------+

Answer 1

尝试这个：

SELECT project, NAME, MAX(desktop) AS desktop, MAX(mobile) AS mobile FROM (
    SELECT project, NAME,
    (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

解释：

首先你对所有数据进行选择（aa），根据平台的内容扩展价值。

然后，您使用该选择作为分组数据的来源。

结果：

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