gistfile1.sql

DROP VIEW OneHop;
DROP VIEW TwoHop;
DROP VIEW ThreeHop;

CREATE VIEW OneHop AS
SELECT dst as airportCode
FROM Flights
WHERE src="PDX";

SELECT name FROM OneHop NATURAL JOIN Airports;

CREATE VIEW TwoHop AS
SELECT dst as airportCode
FROM (SELECT airportCode as src FROM OneHop) NATURAL JOIN Flights;

SELECT DISTINCT name FROM TwoHop NATURAL JOIN Airports;

CREATE VIEW ThreeHop AS
SELECT dst as airportCode
FROM (SELECT airportCode as src FROM TwoHop) NATURAL JOIN Flights;

SELECT DISTINCT name FROM ThreeHop NATURAL JOIN Airports;

SELECT DISTINCT name
FROM (
	 SELECT * FROM ThreeHop UNION
	 SELECT * FROM TwoHop UNION
	 SELECT * FROM OneHop)
NATURAL JOIN Airports;