ค่าโดยสารไปกลับบน CO 1291 จากเดนเวอร์ไปซานฟรานซิสโกและไปกลับคือเท่าไร ไม่จำเป็นต้องใช้ตารางทั้งหมด
what is the round trip fare on CO 1291 from DENVER to SAN FRANCISCO and returnIt is not neccessary to use all the tables.
 airport_service:  city_code [ varchar]  airport_code [ varchar]  miles_distant [ int]  direction [ varchar]  minutes_distant [ int] 
SELECT DISTINCT fare.fare_id FROM airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, city AS CITY_0, city AS CITY_1, fare, flight, flight_fare WHERE ((CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'DENVER' AND CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'SAN FRANCISCO' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND flight.flight_number = 1291) AND NOT fare.round_trip_cost IS NULL AND flight_fare.fare_id = fare.fare_id AND flight.airline_code = 'CO' AND flight.flight_id = flight_fare.flight_id