因此,我有这样的查询:
SELECT curr, from, to, SUM(amount) AS total
FROM transfer
GROUP BY curr, from, to
ORDER BY curr, from
结果如下:
| curr | from | to | total |
| USD | A | B | 1200.00 |
| USD | B | A | 500.00 |
我想要的是:
| curr | from | to | total |
| USD | B | A | 700.00 |
A给B发了1200,B给A寄了