An IS NULL predicate tests for null values in value expressions.
(B)0[m[1mis-null-predicate = [m
[1m [m
[1mqqqq> value-expr qqq> [1;4mIS[m[1m qwqqqqqqqqwq> [1;4mNULL[m[1m qqq> [m
[1m mq> [1;4mNOT[m[1m qj [m
See the Value_Expressions HELP topic for details on value
expressions.
SQL never evaluates an IS NULL predicate as unknown; it is always
true or false. If the value expression is null, SQL evaluates
the predicate as true. If the value expression is not null, the
predicate is false.
Use an IS NULL predicate to retrieve rows with null values in
particular columns. An IS NULL predicate is the only way to
construct a query that includes rows in a result table by testing
whether or not particular columns in the rows have null values.
Other constructions such as NOT LIKE or <> (not equal) do not
include rows with null values in their result tables.