Question

Sample table:

 N  ProductName          Cost          Type            TOTAL

 1  ProductX             3             Checker  
 2  Product0             5             TOY
 3  Product1             5             TOY
 4  Product2             8             TOY

Rows 2,3,4 Need Cost Of Type = Checker + current row cost into the TOTAL column. So row 2 would be 8, 3 would be 8 and 4 would be 11

 5  ProductZ             10            Checker         
 6  Product3             5             TOY
 7  Product4             9             TOY
 8  Product5             18            TOY
 9  Product6             25            TOY

Likewise, these need Cost of ProductZ added to their totals. So Row 6 would be 15, 7 would be 19, and so on. They cannot go back and reference ProductY at row 1.

The datasets are not always the same, and there may be more “Checker” type items in the dataset.

When there’s only one, it works really well, obviously. But when there’s more than one I have issues where the products total is wrong because it’s using the wrong “Checker” value.

Answer 1

I think this query works.

WITH toysAndCheckers AS
(
SELECT n AS toy, (SELECT top 1 lowerCheckers.n From sampleTable AS lowerCheckers
        WHERE lowerCheckers.N < theToys.N
        AND lowerCheckers.[type] = 'Checker'
        ORDER by n desc) AS matchingChecker

FROM sampleTable AS theToys
WHERE theToys.[type] = 'TOY'
),
toyCostAdjustments AS
(SELECT toy, cost AS checkerAdjustment
FROM toysAndCheckers 
JOIN sampleTable
    ON MatchingChecker = n
)       
MERGE sampleTable
USING
toyCostAdjustments
ON n = toy
WHEN MATCHED THEN UPDATE
SET total = cost + CheckerAdjustment
;

The first CTE, “toysAndCheckers”, gets for each toy the N of the CHECKER row that is highest while still being lower than the TOY in question. The second one just replaces the N of the checker with the cheker’s cost. Then you have a straightforward merge. Assuming the N column is unique, you’ll never have multiple matches.