The FROM clause is a mandatory clause in a SelectExpression. It specifies the tables (TableExpression) from which the other clauses of the query can access columns for use in expressions.
FROM TableExpression [ , TableExpression ] *
SELECT Cities.city_id FROM Cities WHERE city_id < 5 -- other types of TableExpressions SELECT TABLENAME, ISINDEX FROM SYS.SYSTABLES T, SYS.SYSCONGLOMERATES C WHERE T.TABLEID = C.TABLEID ORDER BY TABLENAME, ISINDEX -- force the join order SELECT * FROM Flights, FlightAvailability WHERE FlightAvailability.flight_id = Flights.flight_id AND FlightAvailability.segment_number = Flights.segment_number AND Flights.flight_id < 'AA1115' -- a TableExpression can be a joinOperation. Therefore -- you can have multiple join operations in a FROM clause 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