Exam 1z0-071 Topic 3 Question 309 Discussion

C: True. To display the number of products whose PROD_LIST_PRICE is more than the average PROD_LIST_PRICE, you would need to use a subquery to first calculate the average PROD_LIST_PRICE and then use that result to compare each product's list price to the average.
E: True. Displaying products whose PROD_MIN_PRICE is more than the average PROD_LIST_PRICE of all products and whose status is orderable would require a subquery. The subquery would be used to determine the average PROD_LIST_PRICE, and then this average would be used in the outer query to filter the products accordingly.
Subqueries are necessary when the computation of a value relies on an aggregate or a result that must be obtained separately from the main query, and cannot be derived in a single level of query execution.
Reference:
Oracle's SQL documentation provides guidelines for using subqueries in scenarios where an inner query's result is needed to complete the processing of an outer query.