Examine the description of the ORDER_ITEMS table:Examine this incomplete query:SELECT DISTINCT quantity * unit_price total_paid...

In a SELECT statement with DISTINCT, the ORDER BY clause can only order by expressions that are part of the SELECT list.

A. quantity alone is not sufficient to replace <clause> as it is not included in the SELECT list after DISTINCT.

B. This option can successfully replace <clause> because both quantity and unit_price are used in the SELECT expression, and thus their individual values are valid for the ORDER BY clause.

C. total_paid is an alias for the expression quantity * unit_price, but it cannot be used in the ORDER BY clause because Oracle does not allow aliases of expressions in DISTINCT queries to be used in ORDER BY.

D. product_id is not included in the SELECT list after DISTINCT and thus cannot be used in ORDER BY.

E. The expression quantity * unit_price is exactly what is selected, so it can replace <clause> and the query will complete successfully.

References:

Oracle Database SQL Language Reference, 12c Release 1 (12.1): "ORDER BY Clause"