By specifying a NULL predicate, ( null_predicate) you can test whether the value is a NULL value.
<null_predicate>::= <expression> IS [NOT] NULL
Examples
SQL Tutorial, Negative Conditions: NOT
Explanation
The truth content of a NULL predicate is either true or false.
x |
Result of the Function x IS NULL |
---|---|
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).