T SQL CTE Previous Row Calculation - sql

Question

I'm using SQL Server 2016.
I have the below table:
SKU Shop Week ShopPrioirty Replen Open_Stk Open_Stk Calc
111 100 1 1 0 17 NULL
111 200 1 2 2 NULL NULL
111 300 1 3 0 NULL NULL
111 400 1 4 0 NULL NULL
222 100 2 1 5 17 NULL
222 200 2 2 5 NULL NULL
222 300 2 3 5 NULL NULL
222 400 2 4 5 NULL NULL
This is the desired result:
SKU Shop Week ShopPrioirty Replen Open_Stk Open_Stk Calc
111 100 1 1 0 17 17
111 200 1 2 2 NULL 17
111 300 1 3 0 NULL 15
111 400 1 4 0 NULL 15
222 100 2 1 20 17 17
222 200 2 2 15 NULL 12
222 300 2 3 12 NULL 7
222 400 2 4 10 NULL 2
I need to update the 'Open_Stk Calc' based on the previous row:
'Open_Stk Calc' - IIF('Replen'<=IIF('Open_Stk'>=0,'Open_Stk',0),'Replen',0)
I am using a CTE to update a row based on a calculation of the previous rows. This is my SQL:
;WITH CTE AS
(
SELECT
SKU,
[Shop],
[Week],
[Store_Priority],
[Replen],
[Open_Stk],
[Open_Stk Calc],
FIRST_VALUE([Open_Stk]) OVER ( PARTITION BY [SKU] ,[Week] ORDER BY [Store_Priority] ROWS UNBOUNDED PRECEDING)
-
ISNULL(SUM(IIF([Replen] <= IIF([Open_Stk]>=0,[Open_Stk],0),[Replen],0))
OVER (PARTITION BY [SKU] ,[Week] ORDER BY [Store_Priority] ROWS BETWEEN UNBOUNDED PRECEDING AND 1 PRECEDING), 0) AS CurrentStock
FROM [tblTEST])
UPDATE CTE
SET [Open_Stk Calc] = CurrentStock
However, this produces the following result:
SKU Shop Week ShopPrioirty Replen Open_Stk Open_Stk Calc
111 100 1 1 0 17 17
111 200 1 2 2 NULL 17
111 300 1 3 0 NULL 17
111 400 1 4 0 NULL 17
And not the desired result - where have I gone wrong?

Answer 1

As one can see in the MS documentation, the OVER clauses supports specific kind of functions:
Ranking functions
Aggregate functions
Analytic functions
NEXT VALUE FOR function
None of them include IIF, as Luis Cazares noted in their comment.
Your code indicates you do have a clue about what you are doing - maybe you forgot to put your IIF inside a SUM?