CREATE TABLE airports (apid DECIMAL, name TEXT, city TEXT, country TEXT, x DECIMAL, y DECIMAL, elevation DECIMAL, iata TEXT, icao TEXT)
CREATE TABLE airlines (alid DECIMAL, name TEXT, iata TEXT, icao TEXT, callsign TEXT, country TEXT, active TEXT)
CREATE TABLE routes (rid DECIMAL, dst_apid DECIMAL, dst_ap TEXT, src_apid DECIMAL, src_ap TEXT, alid DECIMAL, airline TEXT, codeshare TEXT)

Return the cities with more than 3 airports in the United States.
SELECT city FROM airports WHERE country = 'United States' GROUP BY city HAVING COUNT(*) > 3
SELECT "city" FROM "airports" WHERE "country" = 'United States' GROUP BY "city" HAVING COUNT(*) > 3