Topic group

Indexes are required for linking related tables together in a multiple-table query. To link tables, consider the following issues:

What are the relationships among the tables—one-to-one, one-to-many, many-to-many? For example, an Orders table and a LineItem table are in a one-to-many relationship. The Orders table is the parent table and the LineItem table is the child table.

With related tables, which fields are common among them? To link tables together, you must have an index for the child table on a field that also appears in the parent table. For example, the Orders table and LineItem table both have an ORDER_NO field, and the LineItem table has an index on this field.

Can you use codes instead of long character fields? For example, to link orders in the Orders table to customers in the Customer table, the application uses the customer number, a short character field that uniquely identifies each customer.