Index Tables

Just as an index in a book helps you quickly find information by listing all the pages where a particular topic is discussed, an index in a database table points to all the rows where a particular column value is stored.

An index table helps to quickly locate a record in a database by pointing to a specific column and row in a table. So, for example, to locate a customer in the database, an index on the CUSTOMER table references the Customer Number (account number).

You can use indexes in two ways:

To sequentially access the indexed file.
To directly access individual records in the indexed file based on a given value for the indexed field.