Okay. As you can see, the query did not succeed. So, how can we select some information for those auctions which had their final_price higher than the average final_price? We have to use a subquery. Take a look:

SELECT
  id,
  final_price 
FROM (
  SELECT
    id,
    final_price,
    AVG(final_price) OVER() AS avg_final_price
  FROM auction) c
WHERE final_price > avg_final_price

In the FROM clause, we introduced a subquery where we selected both the final_price for each auction and the average final_price. Because the whole subquery is calculated before the external query, we can use avg_final_price in the external query.