SQL Server adjust each value in a column by another table - sql

Question

I have two tables, TblVal and TblAdj.
In TblVal I have a bunch of values that I need adjusted according to TblAdj for a given TblVal.PersonID and TblVal.Date and then returned in some ViewAdjustedValues. I must apply only those adjustments where TblAdj.Date >= TblVal.Date.
The trouble is that since all the adjustments are either a subtraction or a division, they need to be made in order. Here is the table structure:
TblVal: PersonID, Date, Value
TblAdj: PersonID, Date, SubtractAmount, DivideAmount
I want to return ViewAdjustedValues: PersonID, Date, AdjValue
Can I do this without iterating through TblAdj using a WHILE loop and an IF block to either subtract or divide as necessary? Is there some nested SELECT table magic I can perform that would be faster?

Answer 1

I think you can do it without a loop, but whether you want to or not is another question. A query that I think works is below (SQL Fiddle here). The key ideas are as follows:
Each SubtractAmount has the ultimate effect of subtracting SubtractAmount divided by the product of all later DivideAmounts for the same PersonID. The Date associated with the PersonID isn't relevant to this adjustment (fortunately). The CTE AdjustedAdjustments contains these adjusted SubtractAmount values.
The initial Value for a PersonID gets divided by the product of all DivideAmount values on or after that persons Date.
EXP(SUM(LOG(x))) works as an aggregate product if all values of x are positive. You should constrain your DivideAmount values to assure this, or adjust the code accordingly.
If there are no DivideAmounts, the associated product is NULL and changed to 1. Similarly, NULL sums of adjusted SubtractAmount values are changed to zero. A left join is used to preserve an values that are not subject to any adjustments.
SQL Server 2012 supports an OVER clause for aggregates, which was helpful here to aggregate "all later DivideAmounts."
WITH AdjustedAdjustments AS (
select
PersonID,
Date,
SubtractAmount/
EXP(
SUM(LOG(COALESCE(DivideAmount,1)))
OVER (
PARTITION BY PersonID
ORDER BY Date
ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
)
) AS AdjustedSubtract,
DivideAmount
FROM TblAdj
)
SELECT
p.PersonID,
p.Value/COALESCE(EXP(SUM(LOG(COALESCE(DivideAmount,1)))),1)
-COALESCE(SUM(a.AdjustedSubtract),0) AS AmountAdjusted
FROM TblVal AS p
LEFT OUTER JOIN AdjustedAdjustments AS a
ON a.PersonID = p.PersonID
AND a.Date >= p.Date
GROUP BY p.PersonID, p.Value, p.Date;

Answer 2

Try something like following:
with CTE_TblVal (PersonID,Date,Value)
as
(
select A.PersonID, A.Date, A.Value
from TblVal A
inner join TblAdj B
on A.PersonID = B.PersonID
where B.Date >= A.Date
)
update CTE_TblVal
set Date = TblAdj.Date,
Value = TblAdj.Value
from CTE_TblVal
inner join TblAdj
on CTE_Tblval.PersonID = TblAdj.PersonID
output inserted.* into ViewAdjustedValues
select * from ViewAdjustedValues