| SAS/ACCESS Interface to SYSTEM 2000 Data Management Software: Reference |
Use the following guidelines to determine when to use
a SAS WHERE clause and when to use a SYSTEM 2000 where-clause to specify selection
criteria.
Include a
SYSTEM 2000 where-clause
in your view descriptor when you want to
- restrict users of view descriptors to certain
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 null (missing) values are treated
in the way SYSTEM 2000 expects. (The SYSTEM 2000 style of handling nulls differs
from the SAS style in that SYSTEM 2000 software never regards nulls as equal
to other values, even zero or blank.)
- use the SYSTEM 2000 functionality of the NOT operator.
(The SYSTEM 2000 style of NOT processing differs from the SAS style in that
SYSTEM 2000 includes null values in the answer, where the SAS System may or
may not.)
- 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 SAS WHERE clause when the
previous guidelines do not apply
and you want to
- have more run-time flexibility in subsetting data
- use SAS WHERE clause capabilities that SYSTEM
2000 software does not support, such as arithmetic expressions or truncated
comparisons.
Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
