Task: Text to Code
Input (English): Step 1: For each row in airports table, find the corresponding rows in flights table.
Step 2: find FlightNo of the results of step 1 whose AirportName equals APG
Output (English): SELECT T2.FlightNo FROM airports AS T1 JOIN flights AS T2 ON T1.AirportCode = T2.SourceAirport WHERE T1.AirportName = "APG"