โอ้ มาดูกันว่า EA มีเที่ยวบินจากแอตแลนต้าไปวอชิงตันหรือไม่ ไม่จำเป็นต้องใช้ตารางทั้งหมด
oh let 's see does EA have a flight from ATLANTA to WASHINGTONIt is not neccessary to use all the tables.
 code_description:  code [ varchar]  description [ text] 
SELECT DISTINCT airline.airline_code FROM airline, airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, city AS CITY_0, city AS CITY_1, flight WHERE ((flight.airline_code = 'EA') AND CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'WASHINGTON' AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'ATLANTA' AND flight.airline_code = airline.airline_code AND flight.from_airport = AIRPORT_SERVICE_0.airport_code