NULL is a special value that represents no value. Here are basic rules about NULL values:

► NULL presents no value.

► NULL is not the same as an empty string ''.

► NULL is not the same as a zero value 0.

► NULL can be used as any data type.

► NULL should not be used in any comparison options.

► NULL has its own equality operator "IS".

► NULL has its own not-equality operator "IS NOT".

The tutorial exercise shows you some interesting examples:

SELECT 0 IS NULL FROM DUAL;

0

SELECT 0 IS NOT NULL FROM DUAL;

1

SELECT '' IS NULL FROM DUAL;

0

SELECT '' IS NOT NULL FROM DUAL;

1

SELECT NULL IS NULL FROM DUAL;

1

SELECT NULL IS NOT NULL FROM DUAL;

0