What are all location codes for the delivery locations?
select location_code from delivery_route_locations
Which route has had the fewest orders delivered?
select route_id from order_deliveries as t1 join delivery_route_locations as t2 on t1.location_code = t2.location_code order by t2.route_id limit 1
Which route has the highest number of delivery locations?
select t1.route_name from delivery_routes as t1 join delivery_route_locations as t2 on t1.route_id = t2.route_id group by t1.route_id order by count(*) desc limit 1