IS Condition

IS NULL and IS MISSING are predicates that test for a missing value. IS NULL and IS MISSING are used in the WHERE, ON, and HAVING expressions. Each predicate resolves to true if the SQL expression's result is missing and false if it is not missing.

SAS stores a numeric missing value as a period (.) and a character missing value as a blank space. Unlike missing values in some versions of SQL, missing values in SAS always appear first in the collating sequence. Therefore, in Boolean and comparison operations, the following expressions resolve to true in a predicate:

    3>null
   -3>null
    0>null

The SAS method for evaluating missing values differs from the method of the ANSI standard for SQL. According to the standard, these expressions are NULL. See sql-expression for more information about predicates and operators. See PROC SQL and the ANSI Standard for more information about the ANSI standard.