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

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'