คุณมีเที่ยวบินอะไรบ้างจากบัลติมอร์ไปซานฟรานซิสโกไม่จำเป็นต้องใช้ตารางทั้งหมด
what flights do you have from BALTIMORE to SAN FRANCISCOIt is not neccessary to use all the tables.
 fare_basis:  fare_basis_code [ text]  booking_class [ text]  class_type [ text]  premium [ text]  economy [ text]  discounted [ text]  night [ text]  season [ text]  basis_days [ text] 
SELECT DISTINCT flight.flight_id FROM airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, city AS CITY_0, city AS CITY_1, flight WHERE CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'BALTIMORE' 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