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')
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 = value ) and src_apid in ( select apid from airports where country = value )
Find the number of routes from the United States to Canada .