Database-Management-System

Question 49

Given relations r(w, x) and s(y, z), the result of

    select distinct w, x
    from r, s

is guaranteed to be same as r, provided

A	r has no duplicates and s is non-empty
B	r and s have no duplicates
C	s has no duplicates and r is non-empty
D	r and s have the same number of tuples

Question 49 Explanation:

r has no duplicate, if r can have duplicates it can be remove in the final state. s in non-empty if s is empty then r*s becomes empty.

Correct Answer: A

Question 49 Explanation:

r has no duplicate, if r can have duplicates it can be remove in the final state. s in non-empty if s is empty then r*s becomes empty.