SQL MERGE-Befehl . INSERT aller Datenzeilen verhindern, beschränkbar auf nur geänderte?

MERGE datev_eodb_mandanten_backup AS t
USING datev_eodb_mandanten AS s
ON		t.MDTGUID = s.MDTGUID
AND		t.MDTID = s.MDTID
WHEN	MATCHED
AND (	isnull(t.MDTVON,''1900-01-01 00:00:00.000'') != isnull(s.MDTVON,''1900-01-01 00:00:00.000'')  
OR		isnull(t.MDTBIS,''1900-01-01 00:00:00.000'') != isnull(s.MDTBIS,''1900-01-01 00:00:00.000'')  
OR		isnull(t.MDTSTATUS,0) != isnull(s.MDTSTATUS,0)
OR		isnull(t.MDTNR,0) != isnull(s.MDTNR,0)
OR		isnull(t.MDTNAME,'''') != isnull(s.MDTNAME,'''')  
OR		isnull(t.MDTTYP,'''') != isnull(s.MDTTYP,'''')  
OR		isnull(t.MDTPLZ,'''') != isnull(s.MDTPLZ,'''')  
OR		isnull(t.MDTORT,'''') != isnull(s.MDTORT,'''')  
OR		isnull(t.MDTSTR,'''') != isnull(s.MDTSTR,'''')  
OR		isnull(t.MDTGID,0) != isnull(s.MDTGID,0)
OR		isnull(t.MDTGNAME,'''') != isnull(s.MDTGNAME,'''')  
OR		isnull(t.DOHR,'''') != isnull(s.DOHR,'''') )  
THEN
	UPDATE
	SET		t.MDTVON = s.MDTVON,
			t.MDTBIS = s.MDTBIS,
			t.MDTSTATUS = s.MDTSTATUS,
			t.MDTNR = s.MDTNR,
			t.MDTNAME = s.MDTNAME,
			t.MDTTYP = s.MDTTYP,
			t.MDTPLZ = s.MDTPLZ,
			t.MDTORT = s.MDTORT,
			t.MDTSTR = s.MDTSTR,
			t.MDTGID = s.MDTGID,
			t.MDTGNAME = s.MDTGNAME,
			t.DOHR = s.DOHR
WHEN	NOT MATCHED BY TARGET
THEN
	INSERT(MDTGUID,MDTID,MDTVON,MDTBIS,MDTSTATUS,MDTNR,MDTNAME,MDTTYP,MDTPLZ,MDTORT,MDTSTR,MDTGID,MDTGNAME,DOHR)
	VALUES(s.MDTGUID,s.MDTID,s.MDTVON,s.MDTBIS,s.MDTSTATUS,s.MDTNR,s.MDTNAME,s.MDTTYP,s.MDTPLZ,s.MDTORT,s.MDTSTR,s.MDTGID,s.MDTGNAME,s.DOHR)
WHEN	NOT MATCHED BY SOURCE
THEN
	DELETE;