NULLs are basically for use in database for describe that no value or attributes are exist,
But are not really values themselves. Instead they are just an indicator that a particular field has no value. Some discussions are clarifying that it is better than no value i mean blank value or a default value. we are individually can see little value in a blank field, but default values can be useful. The interesting point about NULLs is that no Primary Key can contain a NULL and thus it\'s useful when comparing Candidate Keys to see if one could potentially contain a NULL, thus disqualifying that key.