Můžete OUTPUT do proměnné tabulky a poté z ní načíst. Zkuste toto:
DECLARE @t table (C1 int, C2 int)
DECLARE @C1 INT, @C2 INT
DECLARE @Output TABLE (DeletedC1 INT, DeletedC2 INT, ActionType VARCHAR(20), InsertedC1 INT, InsertedC2 INT)
set @c1 = 1
set @c2 = 1
MERGE @t as tgt
USING (SELECT @C1, @C2) AS src (C1, C2)
ON (tgt.C1 = src.C1)
WHEN MATCHED AND tgt.C2 != src.C2 THEN
UPDATE SET tgt.C2 = src.C2
WHEN NOT MATCHED BY TARGET THEN
INSERT VALUES (src.C1, src. C2)
OUTPUT deleted.*, $action, inserted.* INTO @Output;
SELECT * FROM @Output WHERE ActionType = 'INSERT'