SELECT route_id
FROM insert_route
WHERE insert_id IN (21,24)
AND
route_id IN (48,49,44,50,55,43,51,25,24,52,47,31,53)
AND
route_id NOT IN
(
SELECT route_id
FROM insert_route
WHERE insert_id IN (12)
)
GROUP BY route_id
HAVING count( DISTINCT insert_id ) = 2