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

Question: How many 'United Airlines' flights depart from Airport 'AHD'?
SQL: SELECT COUNT(*) FROM AIRLINES AS T1 JOIN FLIGHTS AS T2 ON T2.Airline = T1.uid WHERE T1.Airline = "United Airlines" AND T2.SourceAirport = "AHD"