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.
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