1.

What is meant by Null value? What-are the reasons that lead to their occurrence in database relations?

Answer»

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 attributes doesnot apply to an entity. 
  • Value of an attribute is unknown, although it exists. 
  • Unknown because it does not exist.


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