instruction: i wish to book a flight from PITTSBURGH to ATLANTA COACH discount fare
response: 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, fare, fare_basis AS FARE_BASIS_0, fare_basis AS FARE_BASIS_1, flight, flight_fare WHERE (CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'ATLANTA' AND FARE_BASIS_0.class_type = 'COACH' AND FARE_BASIS_1.discounted = 'YES' AND fare.fare_basis_code = FARE_BASIS_0.fare_basis_code AND fare.fare_basis_code = FARE_BASIS_1.fare_basis_code AND flight_fare.fare_id = fare.fare_id AND flight.flight_id = flight_fare.flight_id AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'PITTSBURGH' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code