select   a.route_id, 
         max(case 
               when a.number = b.minnum 
               then a.date 
               else 0 
             end) as startdate, 
         max(case 
               when a.number = b.maxnum 
               then a.date 
               else 0 
             end) as enddate 
from     route_point_tbl a 
         inner join (select   route_id, 
                              max(number) as maxnum, 
                              min(number) as minnum 
                     from     route_point_tbl 
                     group by route_id) b 
           on a.route_id = b.route_id 
group by a.route_id