Question 13 Marks
What is meant by NULL value? What are the reasons that lead to their occurrence in database relations?
Answer
View full question & answer→Null Values: Absence of a data item is represented by a special value called null value. There are three situation which may require the use of null values:
- When a particular attribute does not apply to an entity.
- Value of an attribute is unknown, although it exists.
- Unknown because it does not exist.