Question

The size of a _____ is simply V(A,r) where r is the relation and A is a distinct value

(a) Projection

(b) Outer join

(c) Aggregation

(d) Inner join

The question was posed to me in an interview.

I'm obligated to ask this question of Estimating Statistics of Expression Results topic in section Query Processing and Optimization of RDBMS

Answer 1

Correct answer is (c) Aggregation

Explanation: The size of an aggregation is simply V(A,r) where r is the relation and A is a distinct value since there is one tuple in the aggregation for every distinct value in A.