使用样本数据对单个联接表求和的结果加倍和期望结果的问题。对不起，我现在正在学习MySql-设计可能很糟糕-这就是为什么我想学习如何做得更好，并从这里得到一些建议…员工和帐户表与每个月表定义了一对多的关系…此外，我在每个月表中添加了指向员工和帐户表的外来检查

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使用样本数据对单个联接表求和的结果加倍和期望结果的问题。对不起，我现在正在学习MySql-设计可能很糟糕-这就是为什么我想学习如何做得更好，并从这里得到一些建议…员工和帐户表与每个月表定义了一对多的关系…此外，我在每个月表中添加了指向员工和帐户表的外来检查约束-“名称”两个表中的每个表中的字段都定义为主键。非常感谢您的帮助-我是mysql查询编程的新手，我从来不知道“透视表”

+----+-------------+--+
| ID |    Name     |  |
+----+-------------+--+
|  1 | John Doe    |  |
|  2 | Helen Price |  |
|  3 | John Price  |  |
+----+-------------+--+

+----+---------+--+
| ID |  Name   |  |
+----+---------+--+
|  1 | fisher  |  |
|  2 | fisher1 |  |
+----+---------+--+

+----+-------------+---------+----------+----------+----------+
| ID |    Employee | Account | firstday | seconday | thirdday |
+----+-------------+---------+----------+----------+----------+
|  1 | John Doe    | fisher  |        2 |        4 |        6 | 
|  2 | Helen Price | fisher  |        1 |        1 |        1 | 
|  3 | John Price  | fisher1 |        1 |        2 |        1 | 
|  4 | John Price  | fisher  |        1 |        1 |        1 | 
+----+-------------+---------+----------+----------+----------+

+----+-------------+---------+-----------+----------+-----------+
| ID |    Employee | Account | fourthday | eightday | secondday | 
+----+-------------+---------+-----------+----------+-----------+
|  1 | John Doe    | fisher  |         1 |        4 |         6 |  
|  2 | Helen Price | fisher  |         1 |        1 |         2 |  
|  3 | John Price  | fisher1 |         1 |        2 |         1 |   
|  4 | John Price  | fisher  |         1 |        1 |         1 |    
+----+-------------+---------+-----------+----------+-----------+

   +----+-------------+---------+-----------------+------------------+--------+--+
| ID |  Employee   | Account | January(totals) | February(totals) | Totals |  |
+----+-------------+---------+-----------------+------------------+--------+--+
|  1 | John Doe    | fisher  |              12 |               11 |     23 |  |
|  2 | Helen Price | fisher  |               3 |                4 |      7 |  |
|  3 | John Price  | fisher  |               3 |                3 |      6 |  |
+----+-------------+---------+-----------------+------------------+--------+--+

| ID  | Employee    | Account | January(totals) | February(totals) | Totals |
| --- | ----------- | ------- | --------------- | ---------------- | ------ |
| 1   | John Doe    | fisher  | 12              | 11               | 23     |
| 2   | Helen Price | fisher  | 3               | 4                | 7      |
| 3   | John Price  | fisher  | 3               | 3                | 6      |

SUM(CASE MONTH(date_column) WHEN # THEN amount_column ELSE 0 END) AS MonthTotal

| Employee    | Account | Year | January(totals) | February(totals) | Totals |
| ----------- | ------- | ---- | --------------- | ---------------- | ------ |
| Helen Price | fisher  | 2020 | 3               | 4                | 7      |
| John Doe    | fisher  | 2020 | 12              | 11               | 23     |
| John Price  | fisher  | 2020 | 3               | 3                | 6      |
| John Price  | fisher1 | 2020 | 4               | 4                | 8      |