The earlier results on DB2 and SQL Server have already demonstrated that the database design has the necessary indexes to enable the execution plan that you need, unless the Oracle database is missing indexes that you have on the other databases. Therefore, you could skip this step. However, if you did not already know that they existed, you would check for indexes on Customers(Phone_Number), Orders(Customer_ID), and Order_Details(Order_ID) using the methods of Chapter 3. You can generally take for granted that the primary-key indexes that you need already exist. Look for missing primary-key indexes only when more likely reasons for an incorrect execution plan do not solve the problem and lead you to check for unusual sources of trouble.