Schema: CREATE TABLE Flights (AirportName VARCHAR, AirportCode VARCHAR, SourceAirport VARCHAR, DestAirport VARCHAR); CREATE TABLE Airports (AirportName VARCHAR, AirportCode VARCHAR, SourceAirport VARCHAR, DestAirport VARCHAR)
Question: Find the name of airports which do not have any flight in and out.
SQL: SELECT AirportName FROM Airports WHERE NOT AirportCode IN (SELECT SourceAirport FROM Flights UNION SELECT DestAirport FROM Flights)