PROC SQL: Beyond the Basics Using SAS®

10.5. Indexes and Performance

Indexes can be used to allow rapid access to table rows. Rather than physically sorting a table (as performed by the ORDER BY clause or PROC SORT), an index is designed to set up a logical arrangement for the data without the need to physically sort it. This has the advantage of reducing CPU and memory requirements. It also reduces data access time when using WHERE clause processing (discussed in Section 10.7).

Indexes are useful, but they do have drawbacks. As data in a table is inserted, modified, or deleted, an index must be updated to address the changes. This automatic feature requires additional CPU resources to process any changes to a table. Also, as a separate structure in its own right, an index can consume ...