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; 0SELECT 0 IS NOT NULL FROM DUAL; 1SELECT '' IS NULL FROM DUAL; 0SELECT '' IS NOT NULL FROM DUAL; 1SELECT NULL IS NULL FROM DUAL; 1SELECT NULL IS NOT NULL FROM DUAL; 0