Question: Find the name of airports which do not have any flight in and out.
Schema: 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))
SQL: select airportname from airports where not airportcode in (select sourceairport from flights union select destairport from flights)