SQL using the results from the previous row - sql

Question

I'm trying to do an Excel kind of calculation in SQL. This involves using the closing rate (ClRate) from the previous row and using it to calculate values in the next row. The table starts from 1 Jan and has 1000 rows and each row has known data and data which needs to be calculated (shown in [ ])
Date RecQty RecAmt IssQty IssAmt ClQty ClAmt ClRate
1 Jan - - - - 100 $20,000 200
2 Jan +10 +$2100 -5 [ ] [ ] [ ] [ ]
The calculations to generate the desired result are in the table below
Date RecQty RecAmt IssQty IssAmt ClQty ClAmt ClRate
1 Jan 100 $20,000 200
2 Jan +10 +$2100 -5 -[200*5] [100+10-5] [20,000+2100-200*5] [ClAmt/ClQty]
The IssAmt for each day will be calculated by multiplying the IssQty by the previous days' ClRate. The ClQty is computed as previous day ClQty + current day RecQty - current day IssQty. The ClAmt is computed as previous day ClAmt+ current day RecAmt - current day IssAmt. Finally, the ClRate for each day is computed as ClAmt / ClQty
The only ClRate known is the opening inventory row of the table (1 Jan)- thereafter the ClRate for each subsequent row needs to be computed.
In Excel, you would simply do this calculation by linking the required cells of the previous row and copying/pasting the formula to all the rows below.
How would you do this in SQL? I have tried self joining CTEs, loops and LAG- none of these seems to work. The reason is that the ClRate for each row from 2 Jan onwards is not known - and while Excel can handle computing results on the fly which are used in the following row - SQL is unable to do this.
Seeking help to solve this problem. I'm using SQL Server 2017 and SSMS. If required I can provide the code
Table DDL
CREATE TABLE [Auto].[IronOreTbl](
[Id] [int] NULL,
[Counter] [int] NULL,
[TDate] [date] NOT NULL,
[RecQty] [decimal](16, 2) NULL,
[RecAmt] [decimal](16, 2) NULL,
[IssQty] [decimal](16, 2) NULL,
[IssAmt] [decimal](16, 2) NULL,
[ClQty] [decimal](16, 2) NULL,
[ClAmt] [decimal](16, 2) NULL,
[ClRate] [decimal](16, 2) NULL
) ON [PRIMARY]
GO
INSERT INTO [Auto].[IronOreTbl]
([Id],[Counter],[TDate],[RecQty],[RecAmt],[IssQty],[IssAmt],[ClQty],[ClAmt],[ClRate])
VALUES
(1,0,'2019-01-01',NULL,NULL,NULL,NULL,100,20000,200),
(2,1,'2019-01-02',10,2100,5,NULL,105,NULL,NULL),
(3,2,'2019-01-03',8,1600,2,NULL,111,NULL,NULL),
(4,3,'2019-01-04',20,2400,10,NULL,121,NULL,NULL)
CTE attempts
;WITH ClAmtCTE AS
(
SELECT
Id,RecQty,RecAmt,IssQty,ClQty,ClAmt,ClRate
,EffRate = ClRate
,CumHoldVal= ClAmt
--CAST(ClAmt AS decimal(16,2))
,CumClRt=CAST(ClRate AS decimal(16,2))
,[Counter]
FROM
[Auto].IronOreTbl
WHERE
Id=1
UNION ALL
SELECT
C2.Id,C2.RecQty,c2.RecAmt,C2.IssQty,C2.ClQty,C2.ClAmt,c2.ClRate,
EffRate = (SELECT CumClRt WHERE C2.ID=C2.[Counter]+1),
CumRN =
CAST(
(
CumHoldVal+ISNULL(C2.RecAmt,0)-
(EffRate)*ISNULL(C2.IssQty,0)
)
AS decimal(16,2)
),
CumClRt=CAST(CumHoldVal/C2.ClQty AS decimal(16,2)),
C2.[Counter],
FROM
[Auto].IronOreTbl C2
INNER JOIN ClAmtCTE C1 ON C1.Id = C2.[Counter]

Answer 1

The following code achieves the desired result - while I had got close several days ago, it still took all this time to tie up the last bit; of matching the ClRate with the correct row. There was an additional issue encountered where on days where there are no issues, but only receipts, the rate picked up belonged to the wrong row (I still have no clue why and how this was happening - all I know is that the previous code needed revision to resolve this discrepancy and the modified code attends to the same)
;WITH ClAmtCTE AS
(
SELECT
Id,RecQty,RecAmt,IssQty,ClQty,ClAmt,ClRate
,EffRate = ClRate
,CumHoldVal= ClAmt
--CAST(ClAmt AS decimal(16,2))
,CumClRt=CAST(ClRate AS decimal(16,2))
,[Counter]
FROM
[Auto].IronOreTbl
WHERE
Id=1
UNION ALL
SELECT
C2.Id,C2.RecQty,c2.RecAmt,C2.IssQty,C2.ClQty,C2.ClAmt,c2.ClRate,
EffRate = (SELECT CumClRt WHERE C2.ID=C2.[Counter]+1),
CumRN =
CAST(
(
CumHoldVal+ISNULL(C2.RecAmt,0)-
((SELECT CumClRt WHERE C2.ID=C2.[Counter]+1))*ISNULL(C2.IssQty,0)
)
AS decimal(16,2)
),
CumClRt=CAST((CumHoldVal+ISNULL(C2.RecAmt,0)-
((SELECT CumClRt WHERE C2.ID=C2.[Counter]+1))*ISNULL(C2.IssQty,0))/C2.ClQty AS decimal(16,2)),
C2.[Counter]
FROM
[Auto].IronOreTblC2
INNER JOIN ClAmtCTE C1 ON C1.Id = C2.[Counter]
)
UPDATE [Auto].IronOreTbl
SET ClRate = T1.CumClRt,
ClAmt=CumHoldVal
FROM ClAmtCTE T1
INNER JOIN [Auto].IronOreTbl T2
ON T1.ID = T2.Id
OPTION (MAXRECURSION 0)
Attempting and, in what appears to me as, solving it has taught me several things. Primarily these include:
Calculations which you can set up and run in a heartbeat in a spreadsheet are anything but in SQL
Excel has the ability to both calculate on the fly and utilise results calculated on the fly in the dependent calculations. SQL cannot do this. Having this ability in Excel means you do not have to iterate over the data - once to have Excel compute the results and then for Excel to apply the results where they are needed
For all its use and utility as a data housing medium SQL has a long way to go in attending to standard real world calculations - such as this example; multiple loans, changing interest rates and relevant interest calculations etc etc.