如何从MySql中的另一个字段派生一个字段的值

Question

我有一张表格如下

+---+------------+----------+
| ID| Date       | Amount_1 |
+---+------------+----------+
| 1 | 2016-02-02 |   100.00 |
| 1 | 2016-02-05 |   150.00 |
| 1 | 2016-02-09 |   125.00 |
| 1 | 2016-02-11 |    75.00 |
| 1 | 2016-02-19 |   -46.99 |
| 1 | 2016-02-20 |   -41.33 |
| 1 | 2016-02-29 |   -14.15 |
+---+------------+----------+

我希望在此表格中推导出 Amount_1 中的 Amount_2 ，并且Amount_2的每一行的值必须是上一行和当前行的总和。 Amount_1 列。

我的意思是我想得到下表。

+---+------------+----------+----------+
| ID| Date       | Amount_1 | Amount_2 |
+---+------------+----------+----------+
| 1 | 2016-02-02 |   100.00 |   100.00 |
| 1 | 2016-02-05 |   150.00 |   250.00 |
| 1 | 2016-02-09 |   125.00 |   375.00 |
| 1 | 2016-02-11 |    75.00 |   450.00 |
| 1 | 2016-02-19 |   -46.99 |   403.01 |
| 1 | 2016-02-20 |   -41.33 |   361.68 |
| 1 | 2016-02-29 |   -14.15 |   347.53 |
+---+------------+----------+----------+

Answer 1

试试这样：

SELECT  m.ID, m.Date, m.Amount_1, (@x:=  m.Amount_1 + @x) AS Amount_2
FROM    mytable m,(SELECT @x:=0) c

Answer 2

您可以使用session varable

SET @old_amount = 0;
SELECT ID, Date,Amount_1, (@old_amount := Amount_1 + @old_amount) AS Amount_2
FROM table_name 
ORDER BY date;