Obtenez le nom de jointure par id php

$sql=" SELECT  firm.`name` ,`address_physical_line_1` , `fax_1` , `phone_1` 
       FROM    contactdetails 
       JOIN    firm ON contactdetails.fk_firm_id = firm.id
       WHERE   contactdetails.fk_firm_id = '$id'
     ";

$result = mysql_query($sql);