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