从MySQL的日期范围计算付款

Question

我想在选定的日期内计算付款,但我无法弄清楚如何做到这一点.

这是我表中的示例数据

id    starts_from     payment_per_day
=======================================
1     2012-01-01      10,000.00
2     2012-01-15      10,500.00
3     2012-02-01      11,000.00
4     2012-02-15      11,500.00
5     2012-03-01      12,000.00

我如何计算2012-01-21至2012-02-20的总付款？

总付款应为338,500

from 2012-01-21 to 2012-01-31 = 11 days * 10,500
from 2012-02-01 to 2012-02-14 = 14 days * 11,000
from 2012-02-15 to 2012-02-20 =  6 days * 11,500

但如果我这样做:

SELECT SUM(payment_per_day) as total FROM table 
WHERE starts_from BETWEEN '2012-01-21' AND '2012-02-20'

结果只有22,500

有任何想法吗 ？

Answer 1

SELECT SUM(payment_per_day) as total FROM table 
WHERE starts_from BETWEEN '2012-01-21' AND '2012-02-20';