IS MISSING is a predicate
that tests for a SAS missing value. IS MISSING is used in the WHERE,
ON, and HAVING clauses. The IS MISSING predicate resolves to true
if the result of the SQL expression is a SAS missing value and resolves
to false if it is not a SAS missing value.
The IS MISSING predicate
is valid only in use with SAS native data stores. Only DOUBLE and
CHAR data types support missing values.