How to do an INNER JOIN on multiple columns

Question

I\'m working on a homework project and I\'m supposed to perform a database query which finds flights either by the city name or the airport code, but the flights

Answer 1

Why can't it just use AND in the ON clause? For example:

SELECT *
FROM flights
INNER JOIN airports
   ON ((airports.code = flights.fairport)
       AND (airports.code = flights.tairport))