###HUMAN: list all flights on sunday from SAN FRANCISCO to PITTSBURGH nonstop, ###ASSISTANT: 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, date_day, days, flight WHERE (((flight.stops = 0) AND date_day.day_number = 27 AND date_day.month_number = 8 AND date_day.year = 1991 AND days.day_name = date_day.day_name AND flight.flight_days = days.days_code) AND CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'PITTSBURGH' AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'SAN FRANCISCO' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code