CREATE TABLE airports (dst_apid VARCHAR(255), src_apid VARCHAR(255), apid VARCHAR(255), country VARCHAR(255)); CREATE TABLE routes (dst_apid VARCHAR(255), src_apid VARCHAR(255), apid VARCHAR(255), country VARCHAR(255))
Find the number of routes from the United States to Canada.
    
SQL: 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')