Find the name of airports which do not have any flight in and out.
create table flights (airportname varchar, airportcode varchar, sourceairport varchar, destairport varchar, PRIMARY KEY (airportname)); create table airports (airportname varchar, airportcode varchar, sourceairport varchar, destairport varchar, PRIMARY KEY (airportname))
select airportname from airports where not airportcode in (select sourceairport from flights union select destairport from flights)