GATE | GATE CS 2018 | Question 29

Consider the following two tables and four queries in SQL.

Book (isbn, bname), Stock (isbn, copies)

Query 1:

SELECT B.isbn, S.copies
FROM Book B INNER JOIN Stock S
ON B.isbn = S.isbn;

Query 2:

SELECT B.isbn, S.copies
FROM B B LEFT OUTER JOIN Stock S
ON B.isbn = S.isbn;

Query 3:

SELECT B.isbn, S.copies
FROM Book B RIGHT OUTER JOIN Stock S
ON B.isbn = S.isbn;

Query 4:

SELECT B.isbn, S.copies
FROM B B FULL OUTER JOIN Stock S
ON B.isbn = S.isbn;

Which one of the queries above is certain to have an output that is a superset of the outputs of the other three queries?
(A) Query 1
(B) Query 2
(C) Query 3
(D) Query 4


Answer: (D)

Explanation: In SQL the FULL OUTER JOIN combines the results of both left and right outer joins and returns all (matched or unmatched) rows from the tables on both sides of the join clause.

So, option (D) is correct.

See : Join (Inner, Left, Right and Full Joins), Inner Join vs Outer Join

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