By specifying a NULL predicates (null_predicate), you can test whether the value is a NULL value.
<null_predicate> ::= <expression> IS [NOT] NULL
The truth content of a NULL predicate is either true or false.
|
Result of the x IS NULL function |
x is a NULL value |
true |
x is a special NULL value |
false |
x IS NOT NULL has the same result as NOT(x IS NULL).