DO $$
BEGIN
	 CREATE TEMP TABLE TSrc    ( f1 int, f2 int );
	 CREATE TEMP TABLE TTarget ( f1 int, f2 int );
	 CREATE TEMP TABLE TLog    ( f1 int, f2 int, act int );

	INSERT INTO TSrc VALUES(1,1), (1,3), (1,5), (2,1), (2,5), (2,10);
	INSERT INTO TTarget VALUES(1,3), (1,4), (2,5), (2,6);

	WITH Src AS
	(
		SELECT f1, f2 FROM TSrc				
	),
	Upd AS
	(
		UPDATE TTarget t  SET f2 = s.f2
		FROM	Src s
		WHERE	t.f1 = s.f1 and t.f2 = s.f2
		RETURNING  t.f1, t.f2		
	)
	, INS AS
 	(
		INSERT INTO TTarget (f1, f2)
		SELECT s.f1, s.f2
		FROM  Src s	
		LEFT JOIN Upd u on u.f1 = s.f1 and u.f2 = s.f2
		WHERE u.f1 IS NULL	
--		RETURNING  s.f1, s.f2		-- not the underlying table that the statement modifies
	)

	INSERT INTO TLog
	Select f1, f2, 2 as act from Upd
-- 	UNION
-- 	Select f1, f2, 1 as act from Ins 
	;
END
$$;
Select * from TTarget;
Select * from TLog;