CREATE TABLE Delivery_Routes (route_name VARCHAR, route_id VARCHAR)
CREATE TABLE Delivery_Route_Locations (route_id VARCHAR)

Find the name of route that has the highest number of deliveries.
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
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 NULLS LAST LIMIT 1