( SELECT duration
  FROM calls, gateways
 WHERE calls.id_route = gateways.id_route
   AND gateways.description = 'Ykoz262_Zinzin'
   AND call_start >= NOW() - INTERVAL 2 day
 LIMIT 0, 250 )
UNION
( SELECT 0 as duration
  FROM callsfailed, gateways
 WHERE callsfailed.id_route = gateways.id_route
   AND gateways.description = 'Ykoz262_Zinzin'
   AND call_start >= NOW() - INTERVAL 2 day
 LIMIT 0, 250 )