SAS Certification Prep Guide, 4th Edition

Summary

Using an Index for Efficient WHERE Processing

When processing a WHERE expression, SAS determines whether it is more efficient to access observations sequentially, by examining all observations, or directly, by using an index to access specific observations. Using an index to process a WHERE expression might improve performance and is referred to as optimizing the WHERE expression. By deciding whether to create an index, you play a role in determining which access method SAS can use.

In order to decide whether to use an index, you must evaluate the benefits and costs of using an index.

SAS performs a series of steps to determine whether to process a WHERE expression by using an index or by reading all observations sequentially.