select * from (
( SELECT called_number, call_start, duration, clientsip.login, gateways.description
  FROM calls, clientsip, gateways
  WHERE calls.id_client = clientsip.id_client AND
        calls.id_route = gateways.id_route AND
        calls.client_type=0 AND
        calls.call_start LIKE '2007-05-09%'
) as t1
UNION ALL
( SELECT called_number, call_start, 0 as duration, clientsip.login, gateways.description
  FROM callsfailed as calls, clientsip, gateways
  WHERE calls.id_client = clientsip.id_client AND
        calls.id_route = gateways.id_route AND
        calls.client_type=0 AND
        calls.call_start LIKE '2007-05-09%'
) as t2
) as t3
order by call_start desc