我正在尝试计算车辆的折旧。如果车辆有折扣，我需要停止折旧，根据其影响月份将折价因素考虑在内，然后恢复折旧计算。
车辆每月以2％的固定汇率贬值，其中50个月为100％的贬值点。出现折扣时，我可以停止折旧，但是我不知道如何从某个月开始重新折旧。
下面是在折扣之前直接弃用表的示例：
+----------+-------+------------+--------------+------------+------------+
| Vehicle# | month | depDate | Initial Cost | Monthlydep | totaldep |
+----------+-------+------------+--------------+------------+------------+
| 12451 | 1 | 2015-08-01 | 44953.24 | 899.06 | 899.0648 |
| 12451 | 2 | 2015-09-01 | 44953.24 | 899.06 | 1798.1296 |
| ------- | ----- | ----- | ----- | ----- | ----- |
| 12451 | 42 | 2019-01-01 | 44953.24 | 899.06 | 37760.7216 |
| 12451 | 43 | 2019-02-01 | 44953.24 | 899.06 | 38659.7864 |
+----------+-------+------------+--------------+------------+------------+
那么，我们假设本月（2019-03-01）会出现返利，然后需要从该月起重新计算折旧。我如何从第43个月开始重新计算折旧，而不是整个过程呢？
例如，假设我们在第44个月获得200美元的返利。该表应如下所示：
+----------+-------+------------+--------------+------------+------------+
| Vehicle# | month | depDate | Initial Cost | Monthlydep | totaldep |
+----------+-------+------------+--------------+------------+------------+
| 12451 | 43 | 2019-02-01 | 44953.24 | 899.06 | 38659.7864 |
| 12451 | 44 | 2019-03-01 | 44953.24 | 1099.06 | 39758.8464 |
| 12451 | 45 | 2019-04-01 | 44953.24 | 1099.06 | 40857.9064 |
| 12451 | 46 | 2019-05-01 | 44953.24 | 1099.06 | 41956.9664 |
| 12451 | 47 | 2019-06-01 | 44953.24 | 1099.06 | 43056.0264 |
| 12451 | 48 | 2019-06-01 | 44953.24 | 1099.06 | 44155.0864 |
| 12451 | 49 | 2019-06-01 | 44953.24 | 1099.06 | 45254.1464 |
+----------+-------+------------+--------------+------------+------------+
因此，第49个月将是最后一个月份，因为totalDep等于或高于初始费用
我的示例代码如下。如果删除联合的顶部的第一个cte和联接内部联接，则这是工作折旧计算：
;With cte As( Select bd.[VehicleID]
,Max(bd.[Month]) As month
,Max(DateAdd(DAY,1,EOMONTH(DepreciationReportDate,-1))) As DepreciationReportDate
,Max(bd.MonthlyDepreciation) As MonthlyDepreciation
,Max(bd.AdjustedPurchaseCost) As AdjustedPurchaseCost
,Max(AccumulatedDepreciation) As AccumulatedDepreciation
From Work.dbo.DepreciationSchedule bd
Group By bd.VehicleID
)
,cte_CreateRows As
(
Select bd.[VehicleID]
,bd.[Month]
,DATEADD(DAY,1,EOMONTH(bd.DepreciationReportDate,-1)) As DepreciationReportDate
,bd.MonthlyDepreciation
,bd.AdjustedPurchaseCost
,bd.AccumulatedDepreciation
From Work.dbo.DepreciationSchedule bd
Inner Join cte cte
On cte.VehicleID = bd.VehicleID
And cte.month = bd.Month
Union All
Select bd.[VehicleID]
,[Month] = Cast(cr.[Month]+1 As int)
,DATEADD(DAY,1,EOMONTH(DateAdd(Month, 1, cr.DepreciationReportDate),-1)) As DepreciationReportDate
,bd.MonthlyDepreciation
,bd.AdjustedPurchaseCost
,AccumulatedDepreciation = cr.AccumulatedDepreciation + cr.MonthlyDepreciation
From Work.dbo.DepreciationSchedule bd
Inner Join cte_CreateRows cr On bd.[VehicleID] = cr.[VehicleID]
Where cr.AccumulatedDepreciation < cr.AdjustedPurchaseCost
And DateAdd(Month,1, DateAdd(DAY,1,EOMONTH(cr.DepreciationReportDate,-1))) < DATEADD(DAY,1,EOMONTH(GetDate(),-1))
)
Select a.VehicleID
,a.Month
,a.DepreciationReportDate
,Cast(a.MonthlyDepreciation As Decimal(12,2)) As 'Monthly Depreciation Expense'
,a.AdjustedPurchaseCost
,a.AccumulatedDepreciation
From [cte_CreateRows] As a
Order By a.VehicleID, a.Month