NIELIT 2017 OCT Scientific Assistant A (CS) - Section B: 13

Question

Given relations $R(w,x)$ and $S(y,z),$ the result of 

SELECT DISTINCT $w,x$ from $R,S$

• 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 $S$ has the same number of tuples

Comments

incomplete question

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Should mention equal to r.

Answer 1

The query selects all attributes of R (since we are selecting A, B). Since we have distinct in query, result can be equal to R only if R does not have duplicates.

If we do not give any attribute on which we want to join two tables, then the queries like above become equivalent to Cartesian product. Cartesian product of two sets will be empty if any of the two sets is empty. So, S should have atleast one record to get all rows of R. So, answer is option (a).

Answer 2

ANS : A

R has no duplicates and S is non-empty

Answer 3

answer A . check this https://gateoverflow.in/672/gate-cse-2000-question-2-25