tl; dr：完成的查询是此长解释结尾的最后一个代码块。
让我们逐步讲解，然后将最终解决方案呈现为一个查询。需要几个步骤来解决这个问题。
1）找出哪个酒店我们想要的日期范围涵盖
2）设计一个聪明的方式来选择那些利率
3）结合这些日期和价格以这样的方式给我们，总利息计息。
一些初步的注意
由于利率的实例计算认为天作为其最好的决定，我只是使用的数据类型日期而不是日期时间。如果您需要更高分辨率，请告诉我，我可以更新。
我用以下声明的变量
declare @EndOfTime date = '2049-12-31' -- This is some arbitrary end of time value that I chose
declare @StartDate Date = '2012-04-22' -- I made this earlier to cover more rates
declare @EndDate Date = '2016-04-13'
declare @Amount Float = 100000.00 -- I changed it to a softer number
1）日期间隔
现在，你interest_rates表列出了日期是这样的：
+ ------------- + ----------- +
| interest_rate | incept_date |
+ ------------- + ----------- +
| 10 | 2001-05-03 |
| 11.5 | 2014-01-07 |
| 13.5 | 2016-03-01 |
| 15.5 | 2016-05-01 |
+ ------------- + ----------- +
但你想要它列表的时间间隔是这样的：
+ ------------- + ------------ + ------------ +
| interest_rate | inter_begin | inter_end |
+ ------------- + ------------ + ------------ +
| 10 | 2001-05-03 | 2014-01-06 |
| 11.5 | 2014-01-07 | 2016-02-29 |
| 13.5 | 2016-03-01 | 2016-04-30 |
| 15.5 | 2016-05-01 | 2049-12-31 |
+ ------------- + ------------ + ------------ +
下面的查询可以把你的日期列表为间隔：
select i1.interest_rate
, i1.incept_date as inter_begin
, isnull(min(i2.incept_date) - 1,@EndOfTime) as inter_end
from #interest i1
left join #interest i2 on i2.incept_date > i1.incept_date
group by i1.interest_rate, i1.incept_date
注：我打得有点松的日期算术这里不使用DATEADD（ ）命令。
保持跟踪日期间隔，这样可以更轻松地选择适用的费率。
2）选择在价格
现在，我们可以选择坐我们的期望范围内使用上述查询作为CTE的记录。这个查询有点棘手，所以花点时间去真正理解它。
; with
intervals as (
-- The above query/table
)
select *
from intervals
where inter_begin >= (
select inter_begin -- selects the first rate covered by our desired interval
from intervals
where @StartDate between inter_begin and inter_end
)
and inter_end <= (
select inter_end -- selects the last rate covered by our desired interval
from intervals
where @EndDate between inter_begin and inter_end
)
这有效地过滤掉我们不关心任何率，给我们留下了
+ ------------- + ------------ + ------------ +
| interest_rate | inter_begin | inter_end |
+ ------------- + ------------ + ------------ +
| 10 | 2001-05-03 | 2014-01-06 |
| 11.5 | 2014-01-07 | 2016-02-29 |
| 13.5 | 2016-03-01 | 2016-04-30 |
+ ------------- + ------------ + ------------ +
3）计算利息
现在我们所拥有的一切我们需要，计算利益只是从这张表中选择正确的事情。您为计算所写的大部分内容都保持不变;主要变化在于datediff（）命令。使用@StartDate和@EndDate不会给我们在每个具体费率上花费的精确天数。我们遇到同样的问题，使用inter_begin和inter_end。相反，我们必须使用一个case语句，像
datediff(day,
case when @StartDate > inter_begin then @StartDate else inter_begin end,
case when @EndDate < inter_end then @EndDate else inter_end end
)
在上面的查询将这个东西拿到
; with
intervals as (...) -- same as above
select *
, DATEDIFF(day,
case when @StartDate > inter_begin then @StartDate else inter_begin end,
case when @EndDate < inter_end then @EndDate else inter_end end) as days_active
, @Amount*(POWER((1+interest_rate/100),
convert(float,
DATEDIFF(day,
case when @StartDate > inter_begin then @StartDate else inter_begin end,
case when @EndDate < inter_end then @EndDate else inter_end end
)
)/365.25)
) - @Amount as Actual_Interest
from ... -- same as above
这给了我们这个表
+ ------------- + ------------ + ------------ + ----------- + --------------- +
| interest_rate | inter_begin | inter_end | days_active | Actual_interest |
+ ------------- + ------------ + ------------ + ----------- + --------------- +
| 10 | 2001-05-03 | 2014-01-06 | 624 | 17683.63 |
| 11.5 | 2014-01-07 | 2016-02-29 | 786 | 26283.00 |
| 13.5 | 2016-03-01 | 2016-04-30 | 43 | 1501.98 |
+ ------------- + ------------ + ------------ + ----------- + --------------- +
最后，把这个CTE并取Actual_interest字段的总和：
declare @EndOfTime date = '2049-12-31' -- This is some arbitrary end of time value that I chose
declare @StartDate Date = '2012-04-22' -- I made this earlier to cover more rates
declare @EndDate Date = '2016-04-13'
declare @Amount Float = 100000.00 -- I changed it to a softer number
; with
intervals as (
select i1.interest_rate
, i1.incept_date as inter_begin
, isnull(min(i2.incept_date) - 1,@EndOfTime) as inter_end
from #interest i1
left join #interest i2 on i2.incept_date > i1.incept_date
group by i1.interest_rate, i1.incept_date
)
, interest as (
select *
, DATEDIFF(day,
case when @StartDate > inter_begin then @StartDate else inter_begin end,
case when @EndDate < inter_end then @EndDate else inter_end end) as days_active
, @Amount*(POWER((1+interest_rate/100),
convert(float,
DATEDIFF(day,
case when @StartDate > inter_begin then @StartDate else inter_begin end,
case when @EndDate < inter_end then @EndDate else inter_end end
)
)/365.25)
) - @Amount as Actual_Interest
from intervals
where inter_begin >= (
select inter_begin -- selects the first rate covered by our desired interval
from intervals
where @StartDate between inter_begin and inter_end
)
and inter_end <= (
select inter_end -- selects the last rate covered by our desired interval
from intervals
where @EndDate between inter_begin and inter_end
)
)
select sum(actual_interest) as total_interest
from interest
创建商店d针对这种情况的程序。 –