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SAS Certification Prep Guide, 4th Edition by SAS Institute

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Managing Index Usage

Overview

To manage indexes effectively, it is important to know
  • how SAS decides whether to use an index and which index to use
  • how to determine whether SAS is using an index
  • how to control whether SAS uses an index, or which index it uses.

Understanding How SAS Decides Whether to Use an Index

By default, each time you submit a query (or other SAS program) that contains a WHERE expression, SAS decides whether to use an index, or to read all the observations in the data file sequentially. To make this decision, SAS does the following:
  1. Identifies an available index or indexes.
  2. Estimates the number of rows that would be qualified. If multiple indexes are available, SAS selects the index that it ...

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