如何计算动态天数的滞纳金？

Question

我在做一个收费系统时需要根据不同的日期计算收取它的滞纳金
如：  日期                小计金额         滞纳金金额
2005-10-28             18.50               ?
2006-01-02            568.03               ?
2006-02-08           4562.01               ?假如我是每个月的当月25日开始以%1按天计算滞纳金 ，或者是次月的1日开始计算，该怎么写存储过程了。

Answer 1

declare @t table(日期 datetime,小计金额 numeric(18,2))
insert @t
select '2005-10-28',18.50 union all
select '2006-01-02',568.03 union all
select '2006-02-08',4562.01 union all
select '2006-03-08',1000
select *,
datediff(d,日期,getdate())*0.01 * 小计金额 as 滞纳金金额
from @t/*日期                                                     小计金额                 滞纳金金额                              
------------------------------------------------------ -------------------- ---------------------------------- 
2005-10-28 00:00:00.000                                18.50                24.4200
2006-01-02 00:00:00.000                                568.03               374.8998
2006-02-08 00:00:00.000                                4562.01              1322.9829
2006-03-08 00:00:00.000                                1000.00              10.0000
*/