FROM ???

SELECT Cities.city_id
FROM Cities
WHERE city_id < 5
-- ???????????????
SELECT TABLENAME, ISINDEX 
FROM SYS.SYSTABLES T, SYS.SYSCONGLOMERATES C
WHERE T.TABLEID = C.TABLEID
ORDER BY TABLENAME, ISINDEX
-- ????????????????????????
SELECT *
FROM Flights, FlightAvailability
WHERE FlightAvailability.flight_id = Flights.flight_id
AND FlightAvailability.segment_number = Flights.segment_number
AND Flights.flight_id < 'AA1115'
-- ???????????????????????????????????????????????????
--??????????????????FROM?????????????????????????????????????????????????????????
SELECT COUNTRIES.COUNTRY, CITIES.CITY_NAME, FLIGHTS.DEST_AIRPORT
FROM COUNTRIES LEFT OUTER JOIN CITIES
ON COUNTRIES.COUNTRY_ISO_CODE = CITIES.COUNTRY_ISO_CODE
LEFT OUTER JOIN FLIGHTS
ON Cities.AIRPORT = FLIGHTS.DEST_AIRPORT