Table schema:
CREATE TABLE AIRLINES (Airline VARCHAR, uid VARCHAR); CREATE TABLE FLIGHTS (Airline VARCHAR, SourceAirport VARCHAR)

Question: Find all airlines that have flights from airport 'CVO' but not from 'APG'.
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"