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"
Find all airlines that have flights from airport 'CVO' but not from 'APG'.
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 ''
select t1 . airline from airlines as t1 join flights as t2 on t1 . uid = t2 . airline where t2 . sourceairport = value except select t1 . airline from airlines as t1 join flights as t2 on t1 . uid = t2 . airline where t2 . sourceairport = value
Find all airlines that have flights from airport 'CVO ' but not from 'APG ' .