Advanced Topics for Users

Specifying Selection Criteria

The following guidelines will help you to determine when to use a WHERE clause in SAS and when to use a SYSTEM 2000 where-clause to specify selection criteria.

Use a SYSTEM 2000 where-clause in your view descriptor when you want to

restrict users of view descriptors to specific subsets of data.
use SYSTEM 2000 syntax and functionality, such as component names, stored strings, HAS, AT, and the NON-KEY specification.
qualify using a database item that is not in the view descriptor.
ensure that nulls (missing values) are treated in the way SYSTEM 2000 expects. (The SYSTEM 2000 handling of nulls differs from SAS in that SYSTEM 2000 does not treat nulls as equal to other values, including other nulls.)
use the SYSTEM 2000 functionality of the NOT operator. (The SYSTEM 2000 processing of the NOT operator differs from SAS in that SYSTEM 2000 includes null values in the answer, where SAS might or might not include nulls.)
prevent users from sequentially passing the entire database. (The DBA can also set the SYSTEM 2000 option to DISABLE FULL PASSES as a way of preventing sequential processing.)

Use a WHERE clause in SAS when the preceding guidelines do not apply, and you want to

have more run-time flexibility in subsetting data
use WHERE clause capabilities in SAS that SYSTEM 2000 does not support, such as arithmetic expressions or truncated comparisons

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