You can not force it, you can encourage it. If you specify the name of a logical file in an SQL request, you are actually making the system work harder to fulfill the request. The operating system needs to know the name of the physical file. If you tell it a logical file, it needs to figure out the name and location of the physical.

Once the physical file is known, the operating system goes through a similar process to what we described earlier. It looks at the key fields of all dependent files on the system and attempts to find an existing index matching the fields in the WHERE clause of the SQL request. This is called query optimization and the building of an access plan. The operating system determines on its own what index to use based on its optimization logic and the syntax of the SQL provided.