SQL Update where select top(num) - sql

Question

I want to UPDATE a column in the same table based on if 4 records are returned by the subquery.
This is the table structure
Id Form Quantity Transitdays percentUnderQty percentOverQty
192 0 15500 5 13950 17050
193 0 1250 5 1125 1375
194 0 5000 5 4500 5500
195 0 12500 4 11250 13750
196 0 164250 3 147825 180675
197 0 5250 3 4725 5775
198 0 6250 3 5625 6875
199 0 12250 3 11025 13475
200 0 1750 2 1575 1925
201 0 17000 2 15300 18700
202 0 2500 2 2250 2750
203 0 11500 2 10350 12650
204 0 1250 1 1125 1375
This is my attempt so far. This statement is updating all of the records and not just specific ones based on the subquery.
UPDATE Temp_Runlist
SET Form = (
SELECT MAX(Quantity) + 1 AS Form
FROM Temp_Runlist AS t2
)
WHERE EXISTS (
SELECT TOP (4) Quantity
FROM Temp_Runlist AS t1
WHERE (Quantity BETWEEN 1125 AND 1375) AND (Form = 0)
)
Logic Explanation:
I will loop over each quantity and call this query. The query should update the Form column with values starting at 1. In the query example below the result should be that the query would not update form because the subquery only found 2 matching records. If the subquery returned 4 records then the Form column of those 4 records would be 1. On the next pass then form would be 2 if only the subquery returns four matches.

Answer 1

Maybe there's a better way, but I think it would be easiest to use a temp table to hold the ids you want to update and use more than one statement. For example:
WITH CTE AS (
SELECT TOP (4) Id
FROM Temp_Runlist AS t1
WHERE (Quantity BETWEEN 1125 AND 1375) AND (Form = 0)
)
SELECT Id INTO #tmpIDs FROM CTE;
GO
IF (SELECT COUNT(Id) FROM #tmpIDs) = 4
BEGIN
UPDATE Temp_Runlist
SET Form = (
SELECT MAX(Form) + 1 AS Form
FROM Temp_Runlist AS t2
)
WHERE Id IN (SELECT Id FROM #tmpIDs)
END;
GO
DROP TABLE #tmpIDs
GO
The CTE gathers the records you want.
The IF checks to see if there are actually 4 records.
Then the UPDATE uses the temp table of Ids to limit.
BTW - your example had MAX(Quantity), when it looks like it should be MAX(Form).