Running slow with intersect - sql

Question

Trying to optimize a query it is updaing the records in table A based on the INTERSECT on two data sets.
UPDATE #TableA
SET IsFlag = CASE WHEN ISNULL(RJobFlag, 0) > 0 THEN 0 ELSE 1 END
FROM #TableA AS ABC
OUTER APPLY (
SELECT 1 RJobFlag
WHERE EXISTS (
SELECT ABC.COLUMN1,ABC.COLUMN2,ABC.COLUMN3,ABC.COLUMN4,ABC.COLUMN5,ABC.COLUMN6,ABC.COLUMN7,ABC.COLUMN8,ABC.COLUMN8,ABC.COLUMN9,ABC.COLUMN10,StudentID,SubjectID
INTERSECT
SELECT XYZ.COLUMN1,XYZ.COLUMN2,XYZ.COLUMN3,XYZ.COLUMN4,XYZ.COLUMN5,XYZ.COLUMN6,XYZ.COLUMN7,XYZ.COLUMN8,XYZ.COLUMN8,XYZ.COLUMN9,XYZ.COLUMN10,StudentID,SubjectID
FROM #TableB AS XYZ
WHERE XYZ.COLUMN1 = (SELECT DISTINCT ID FROM #TableC MNOP WHERE MNOP.StudentID = ABC.StudentID)
AND StudentID = ABC.StudentID
AND SubjectID = ABC.SubjectID )
) Subquery
WHERE ABC.COLUMN1= '2'
Appretiated if you have some ideas to better optimize it.
Thanks

Answer 1

This might be worse never know.
UPDATE tA
SET IsFlag = COALESCE(RJobFlag, 0)
FROM #TableA tA
LEFT JOIN ( SELECT 1 RJobFlag, *
FROM #TableB tB
WHERE EXISTS ( SELECT *
FROM #TableC tC
WHERE tC.ID = tB.COLUMN1 AND tC.StudentID = tB.StudentID)
) tB
ON tA.StudentID = tB.StudentID
AND tA.SubjectID = tB.SubjectID
AND tA.COLUMN1 = tB.COLUMN1
AND tA.COLUMN2 = tB.COLUMN2
AND tA.COLUMN3 = tB.COLUMN3
AND tA.COLUMN4 = tB.COLUMN4
AND tA.COLUMN5 = tB.COLUMN5
AND tA.COLUMN6 = tB.COLUMN6
AND tA.COLUMN7 = tB.COLUMN7
AND tA.COLUMN8 = tB.COLUMN8
AND tA.COLUMN9 = tB.COLUMN9
AND tA.COLUMN10 = tB.COLUMN10
If #TableA has a bunch of records and you're using outer apply or outer join every time you update it will be slow since it has to update every single record. maybe there's a way to only update the records that have changed?