มีการขนส่งภาคพื้นดินประเภทใดในเดนเวอร์ไม่จำเป็นต้องใช้ตารางทั้งหมด
what kind of ground transportation is there in DENVERIt is not neccessary to use all the tables.
 restriction:  restriction_code [ text]  advance_purchase [ int]  stopovers [ text]  saturday_stay_required [ text]  minimum_stay [ int]  maximum_stay [ int]  application [ text]  no_discounts [ text] 
SELECT DISTINCT ground_service.transport_type FROM city, ground_service WHERE city.city_name = 'DENVER' AND ground_service.city_code = city.city_code