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Chapter 6
Note on Discarding Records
When usin g a Select node to discard records, note that syntax uses three-valued logic and
automatically includes null values i n select statements. To ex clude null values ( system-missing)
in a sele ct expression, you must explicitl y specify this by us ing and not in the expression . For
example, to select and include all records where the type of prescription drug is Drug C, you
would use the follow ing select statemen t:
Drug = 'drugC' and not(@NULL(Drug))
Earlier versions of excluded null values in such situations.