I keep getting this error when I tried to execute this query, although I couldn't figure out what went wrong. I'm using Oracle and JDBC. Here's the query: SELECT Temp.flight_number, Temp.avgprice FROM (SELECT P.flight_number, AVG (P.amount) AS avgprice FROM purchase P GROUP BY P.flight_number) AS Temp WHERE Temp.avgprice = (SELECT MAX (Temp.avgprice) FROM Temp) I'm trying to get the maximum of average price of the tickets that customers have booked, group by flight_number.