Something

UPDATE trs_phx.prod_dial_def a
SET a.dial_def_index = (
	SELECT b.dial_def_index
	FROM trs_phx.prod_dial_def b
	WHERE a.switch_id=103 AND b.switch_id=101 AND
		 a.DIAL_SERVICES=b.DIAL_SERVICES AND
		 a.CARRIER_CODE=b.carrier_code AND
		 a.ORIGIN_TYPE=b.ORIGIN_TYPE AND
		 a.prod_id=b.prod_id AND
		 a.DIAL_DEF_INDEX!=b.DIAL_DEF_INDEX )


ORA-01407: cannot update ("TRS_PHX"."PROD_DIAL_DEF"."DIAL_DEF_INDEX") to NULL