SQL查询按月返回分组列的总和，包括所有之前的日期

Question

我想回报按月汇总账户的余额，按帐户和月份分组。例如，给定一个交易表，看起来像这样：

| date  | account_id | trans_amount | 
| 2012-01-01 |   1 |  -2500 | 
| 2012-01-01 |   2 |  -2500 | 
| 2016-01-01 |   1 |   5000 | 
| 2016-01-01 |   2 |   5000 | 
| 2016-02-01 |   1 |   7500 | 
| 2016-02-01 |   2 |   7500 | 

我想查询返回：

| month | year | account_id | balance | 
| 01 | 2012 |   1 | -2500 | 
| 01 | 2012 |   2 | -2500 | 
| 01 | 2016 |   1 | 2500 | 
| 01 | 2016 |   2 | 2500 | 
| 02 | 2016 |   1 | 10000 | 
| 02 | 2016 |   2 | 10000 | 

我开始用这样的：

SELECT MONTH(date), YEAR(date), account_id, SUM(trans_amount) 
FROM transactions 
GROUP BY account_id, MONTH(date), YEAR(date); 

当然，但在分组期间给出了变化，而不是包括期间之前的交易在内的余额。

Answer 1

最简单的方法将是一个嵌套查询。类似这样的：

SELECT MONTH(date) as month, YEAR(date) as year, account_id, (select SUM(trans_amount) from transactions t2 where t1.date>=t2.date and t1.account_id = t2.account_id) as balance 
FROM transactions t1 
GROUP BY account_id, MONTH(date), YEAR(date); 

您很可能需要修复一些语法。我也不完全确定日期与分组的匹配程度，因此您可能需要为内部选择构建合成日期。