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)
CREATE TABLE airports (apid DECIMAL, name TEXT, city TEXT, country TEXT, x DECIMAL, y DECIMAL, elevation DECIMAL, iata TEXT, icao TEXT)

How many different cities do have some airport in the country of Greenland?
SELECT COUNT(DISTINCT city) FROM airports WHERE country = 'Greenland'
SELECT COUNT(DISTINCT "city") FROM "airports" WHERE "country" = 'Greenland'