User's Manual

104
Chapter 6
Note on Discarding Records
When usin g a Select node to discard records, note that syntax uses three-valued logic and
automatically inc ludes null values in select statements. To exclude null values (system-missing)
in a select expression, you must explicitly specify this by using and not in the e xpression . For
example, to select and include all records where the type of prescription drug is Drug C, you
would use the follow ing select statement:
Drug = 'drugC' and not(@NULL(Drug))
Earlier versions of exc luded null values in such situations.