มีกี่เที่ยวบินที่มาจากเดนเวอร์ถึงบัลติมอร์ในวันที่ 7 19ไม่จำเป็นต้องใช้ตารางทั้งหมด
how many flights come from DENVER to BALTIMORE on 7 19It is not neccessary to use all the tables.
 days:  days_code [ varchar]  day_name [ varchar] 
SELECT COUNT(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.arrival_time < flight.departure_time) AND date_day.day_number = 18 AND date_day.month_number = 7 AND date_day.year = 1991 AND days.day_name = date_day.day_name AND flight.flight_days = days.days_code) OR (date_day.day_number = 19 AND date_day.month_number = 7 AND date_day.year = 1991 AND days.day_name = date_day.day_name AND flight.flight_days = days.days_code AND NOT (flight.arrival_time < flight.departure_time))) AND (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 = 'BALTIMORE' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code AND flight.to_airport = AIRPORT_SERVICE_1.airport_code)