How to update the column without loop in SQL Server? - sql-server

Question

Due to performance perspective I just need to remove loop and using some joins or other solution to update the data in #Result table and get the same result which return by loop.
Scalar function:
CREATE FUNCTION [MultiplyerScl]
(#a INT, #b INT)
RETURNS INT
AS
BEGIN
DECLARE #i AS INT = 2
DECLARE #Value AS INT
IF (#b % #a = 0)
BEGIN
SET #Value = #b
END
ELSE
BEGIN
WHILE (1=1)
BEGIN
IF((#b * #i) % #a = 0)
BEGIN
SET #Value = #b * #i
BREAK;
END
ELSE
BEGIN
SET #i = #i + 1
END
END
END
RETURN #Value
END
Table design and its value.
CREATE TABLE #NUM (Groupid INT, GroupValue INT)
INSERT INTO #NUM
VALUES (1, 8), (1, 9), (1, 23), (2, 5), (2, 5), (2, 10)
Main for loop logic.
SELECT
Groupid,
GroupValue,
MaxValue = MAX(GroupValue) OVER (PARTITION BY Groupid),
MaxCount = COUNT(1) OVER(),
RID = ROW_NUMBER() OVER (ORDER BY groupid)
INTO
#Result
FROM
#NUM
DECLARE #i AS INT = 1
DECLARE #RawCnt AS INT = (SELECT MAX(MaxCount) FROM #Result)
DECLARE #iGroupid INT
DECLARE #iGroupvalue INT
DECLARE #iMaxValue INT
WHILE(#i <= #RawCnt)
BEGIN
SELECT
#iGroupid = Groupid,
#iGroupvalue = Groupvalue,
#iMaxValue = MaxValue
FROM
#Result
WHERE
RID = #i
UPDATE #Result
SET MaxValue = dbo.[MultiplyerScl](#iGroupvalue, #iMaxValue)
WHERE Groupid = #iGroupid
SET #i = #i + 1
END
SELECT * FROM #Result

Answer 1

Try this out
SELECT
Groupid,
GroupValue,
MaxValue = MAX(GroupValue) OVER (PARTITION BY Groupid),
MaxCount = COUNT(1) OVER(),
RID = ROW_NUMBER() OVER (ORDER BY groupid)
INTO
#Result
FROM
#NUM
;WITH Res AS
(
SELECT Groupid, e.Groupvalue, dbo.[MultiplyerScl](Groupvalue, e.MaxValue) AS
MaxValue, 1 AS i
FROM #Result e
UNION ALL
--recursive execution
SELECT e.Groupid, m.Groupvalue, dbo.[MultiplyerScl](e.Groupvalue, m.MaxValue) AS MaxValue, m.i + 1 AS i
FROM #Result e
INNER JOIN Res m ON e.Groupid = m.Groupid
WHERE dbo.[MultiplyerScl](e.Groupvalue, m.MaxValue) > m.MaxValue
)
SELECT Groupid, MAX(MaxValue) AS MaxValue
INTO #FinalResult
FROM Res
GROUP BY Groupid
UPDATE re
SET re.MaxValue = ire.MaxValue
FROM #FinalResult ire
INNER JOIN #Result re ON re.Groupid = ire.Groupid
SELECT * FROM #Result