SAS Certification Prep Guide, 4th Edition

Chapter 23: Querying Data Efficiently

1. Correct answer: d

   When using an index to select a subset, SAS loads only the pages that contain at least one qualified observation into input buffers. When accessing observations sequentially, SAS must load all pages into input buffers. Loading more pages requires more I/O operations.
2. Correct answer: b

   SAS does not use an index for a WHERE condition that contains a function other than TRIM or SUBSTR.
3. Correct answer: a

   The size of the subset relative to the size of the data set is an important factor in determining which access method is most efficient. If a subset is large (more than 33% of the data set), it is likely to be more efficient to use sequential access than direct access. Direct ...