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

Find the number of routes from the United States to Canada.
SELECT COUNT(*) FROM routes WHERE dst_apid IN (SELECT apid FROM airports WHERE country = 'Canada') AND src_apid IN (SELECT apid FROM airports WHERE country = 'United States')
SELECT COUNT(*) FROM "routes" WHERE "dst_apid" IN (SELECT "apid" FROM "airports" WHERE "country" = 'Canada') AND "src_apid" IN (SELECT "apid" FROM "airports" WHERE "country" = 'United States')