GATE CS 2026 Set 1 — Question 43
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Databases → Relational Model → Joins
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Question
Consider a relational database schema with two relations
R(P, Q) and S(X, Y).Let be a tuple relational calculus expression.Which one of the following relational algebraic expressions is equivalent to ?Correct answer
(B) _P (S _(S.X=R.Q) R)
Solution
The tuple relational calculus expression is given by:This expression selects tuples such that there exists a where is in and there exists a where is in .In relation
In relation
R(P, Q), the tuple is , so and .In relation
S(X, Y), the tuple is , so and .The join condition is on the common value , which corresponds to and . Thus, the join condition is (or ).The result requires the attribute corresponding to , which is (or just since the schema is R(P,Q)).Translating to relational algebra:1.Perform a natural join or equijoin between and on the condition .
2.Project the attribute from the result.
Expression: or equivalently .Option (B) matches this exactly: .Continue learning with Success Tracker
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