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Indexes make it easier and faster to process information in a table. With multiple tables, indexes are also necessary to link related tables together. Most tables should have at least one index, to organize rows and link to related tables, but too many indexes can slow performance.

To identify which fields to index, ask the following questions:

What will users know when they search for information? For example, in the dive shop tables, users might want to search for a customer name, customer number, order number, or order date. Consider indexing on these fields.

What are the common threads that tie the information together? For example, a customer number could be a common field between the Orders table and the Customer table, and the order number could be a common field between the Orders table and the Lineitem table.