SQL查詢按月返回分組列的總和，包括所有之前的日期

Question

我想回報按月彙總賬戶的餘額，按帳戶和月份分組。例如，給定一個交易表，看起來像這樣：

| 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 | 

我想查詢返回：

| 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 | 

我開始用這樣的：

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

當然，但在分組期間給出了變化，而不是包括期間之前的交易在內的餘額。

Answer 1

最簡單的方法將是一個嵌套查詢。類似這樣的：

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); 

您很可能需要修復一些語法。我也不完全確定日期與分組的匹配程度，因此您可能需要爲內部選擇構建合成日期。