Question

What is the function of the union operation?

(a) It combines the results of any two different queries

(b) It combines the results of two different queries which have the same set of attributes in the select clause

(c) It combines the results of two different queries which have the same condition in the where clause

(d) It gives the Cartesian product of the results of any 2 queries

This question was addressed to me in a national level competition.

This intriguing question originated from Set Operations topic in division Introduction to Relational Model and Sql of RDBMS

Answer 1

Correct option is (b) It combines the results of two different queries which have the same set of attributes in the select clause

Easiest explanation: The union operation combines the results of two different queries which have the same set of attributes in the select clause. It automatically eliminates duplicates.