How to use different sub queries with SQL MERGE - sql

Question

Can we pass different sub queries in SQL MERGE for inserting and updating data?
MERGE TableA AS SOURCE
USING TbaleB AS TARGET
ON (SOURCE.ID=TARGET.ID)
WHEN NOT MATCHED BY TARGET
THEN INSERT(COLUMN1, COLUMN2,COLUMN3 )
SELECT * FROM TableC
WHEN MATCHED
THEN UPDATE COLUMN1=SOURCE.Column1, COLUMN2=SOURCE.Column2,COLUMN3=SOURCE.Column3
FROM Table4
INNER JOIN INNER JOIN Table5
ON Table4.ID=Table5.ID
WHERE Table5.ID=1
OUTPUT $action, inserted.*;
Is there any other option to do this?
EDIT:
Using below script to create tables, insert data,
CREATE TABLE TableA([ID] [int] IDENTITY(1,1) NOT NULL,
ColumnA [nvarchar](50) NULL,
ColumnB [nvarchar](50) NULL,
ColumnC [nvarchar](50) NULL,
) ON [PRIMARY]
CREATE TABLE TableB([ID] [int] IDENTITY(1,1) NOT NULL,
ColumnA [nvarchar](50) NULL,
ColumnB [nvarchar](50) NULL,
ColumnC [nvarchar](50) NULL,
) ON [PRIMARY]
Insert into TableA values('A','1','W')
Insert into TableA values('A','2','X')
Insert into TableA values('B','1','Y')
Insert into TableB values('A','1','U')--To be update
Insert into TableB values('B','2','N')--New row to insert
Used below query to insert:
SELECT Source.* INTO #tempTable
FROM (SELECT row_number() OVER ( PARTITION BY ColumnA,ColumnB ORDER BY ColumnA,ColumnB ) Row_ID, * --using row_number to remove duplicate rows
FROM TableB) Source
LEFT OUTER JOIN TableA Target
ON Source.ColumnA = Target.ColumnA AND Source.ColumnB = Target.ColumnB
WHERE Row_ID=1 AND Target.ColumnB IS NULL AND Target.ColumnB IS NULL
ALTER TABLE #tempTable drop column Row_ID, ID
INSERT INTO TableA(ColumnA,ColumnB ,ColumnC)
select * from #tempTable
Used below query to update existing record:
UPDATE Target SET Target.ColumnC =Source.ColumnC
FROM TableA Target
INNER JOIN TableB AS Source
ON Source.ColumnA = Target.ColumnA AND Target.ColumnB = SOURCE.ColumnB
And I need the output as
ID ColumnA ColumnB ColumnC
4 A 1 U
5 A 2 X
6 B 1 Y
7 B 2 N
It is working fine, but for performance perpose, can we do the same by using MERGE?

Answer 1

Try the following:
WITH S AS
(
SELECT
B.ColumnA, B.ColumnB, B.ColumnC
FROM
(
SELECT
B.ColumnA, B.ColumnB, B.ColumnC,
ROW_NUMBER() OVER (PARTITION BY B.ColumnA, B.ColumnB ORDER BY B.ColumnA, B.ColumnB) AS RowId
FROM TableB B
) B
WHERE
B.RowId = 1
)
MERGE
TableA T
USING
S ON T.ColumnA = S.ColumnA AND T.ColumnB = S.ColumnB
WHEN NOT MATCHED BY TARGET
THEN INSERT (ColumnA, ColumnB, ColumnC)
VALUES (S.ColumnA, S.ColumnB, S.ColumnC)
WHEN MATCHED AND
(S.ColumnC <> T.ColumnC OR S.ColumnC IS NULL AND T.ColumnC IS NOT NULL OR S.ColumnC IS NOT NULL AND T.ColumnC IS NULL)
THEN UPDATE SET T.ColumnC = S.ColumnC;