Database: flight_2
Question: Which airlines have departures from CVO but not from APG airports?
SQL: select t1.airline from airlines as t1 join flights as t2 on t1.uid  =  t2.airline where t2.sourceairport  =  "cvo" except select t1.airline from airlines as t1 join flights as t2 on t1.uid  =  t2.airline where t2.sourceairport  =  "apg"