Question

If the attribute phone number is included in the relation all the values need not be entered into the phone number column. This type of entry is given as

(a) 0

(b) –

(c) Null

(d) Empty space

The question was posed to me in a job interview.

I would like to ask this question from Null Values Operations topic in section SQL : Queries, Constraints and Triggers of Database Management

Answer 1

The correct answer is (c) Null

Easiest explanation - Null is used to represent the absence of a value.