Records in a table are indexed by the primary key of the table. For example, a customer record is indexed by the key CUSTOMER_NUMBER. As a rule, the customers are displayed in the order of the key field.
Records can also be indexed by tables higher in the table structure. For example, the CUSTOMER_NUMBER is included as a secondary key in the ORDER_HEADER table. This allows order records to be indexed in customer sequence.
If you want to index the records in a table by a key other than the primary key of the table, you define an index-only table that uses the desired key as its primary key. It is not necessary to do this where one of the other data tables already uses this key.
For example, to view the records on the CUSTOMER table in order of the customer name, an index-only table can be used. This table defines CUSTOMER_NAME as the key field on the table:
The index-only table is a parent table of the CUSTOMER table, and allows the customer records to be viewed in name order.