MYSQL Select 多列取决于特定列

Question

我想做一个 SELECT 请求根据平台值设法获得 2 列值（桌面和移动）。

这是一个例子table:

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

试试这个：

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：

首先你对所有数据做一个选择(aa)，根据平台的内容来扩展价值。

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

MYSQL Select 多列取决于特定列

MYSQL Select multiple columns depending on a specific column

mysql

select

merge

group-by

nested-select