mysql - MySQL - 具有计算关系的 PHP SELECT 表

Question

我有这张表：

+------------+-----------+--------+-------+------------+
|  username  | exam_code | module | value | percentage |
+------------+-----------+--------+-------+------------+
|    aaaaa   |     x     |    1   |   60  |      -     |
|    aaaaa   |     x     |    2   |   80  |      -     |
|    aaaaa   |     x     |    3   |   70  |      -     |
|    bbbbb   |     x     |    1   |   60  |      -     |
|    bbbbb   |     x     |    2   |   70  |      -     |
|    bbbbb   |     x     |    3   |   90  |      -     |
+------------+-----------+--------+-------+------------+

我想输入自己（使用 php POST），模块的百分比。
例如，如果我输入module 1 = 50%, module 2 = 35%, module 3 = 15%
（总数为 100）

它将把以前的表格变成：

+------------+-----------+--------+-------+------------+
|  username  | exam_code | module | value | percentage |
+------------+-----------+--------+-------+------------+
|    aaaaa   |     x     |    1   |   60  |     50     |
|    aaaaa   |     x     |    2   |   80  |     35     |
|    aaaaa   |     x     |    3   |   70  |     15     |
|    bbbbb   |     x     |    1   |   70  |     50     |
|    bbbbb   |     x     |    2   |   70  |     35     |
|    bbbbb   |     x     |    3   |   90  |     15     |
+------------+-----------+--------+-------+------------+

直到这一行，我可以用 PHP 做到这一点

我想问的是，如何将这个表（在输入百分比字段后）变成这个

+------------+----------+----------+----------+
|  username  | module 1 | module 2 | module 3 |
+------------+----------+----------+----------+
|    aaaaa   |     30   |    28    |   10.5   |
|    bbbbb   |     35   |    24.5  |   13.5   |
+------------+----------+----------+----------+

（解释）

+------------+----------+----------+----------+
|  username  | module 1 | module 2 | module 3 |
+------------+----------+----------+----------+
|    aaaaa   | (60x50%) | (80x35%) | (70x15%) |
|    bbbbb   | (70x50%) | (70x35%) | (90x15%) |
+------------+----------+----------+----------+

如何SELECT（不创建表）获取此表，仅使用 MySQL 语法？

Answer 1

像这样的事情应该这样做。

SELECT username, 
  SUM(CASE WHEN module = 1 THEN value*percentage/100 END) as module1,
  SUM(CASE WHEN module = 2 THEN value*percentage/100 END) as module2,
  SUM(CASE WHEN module = 3 THEN value*percentage/100 END) as module3
FROM tablename
GROUP BY username

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