SELECT operation in SQL is equivalent to A) the selection operation in relational algebra B) the selection operation in relational algebra, except that SELECT in SQL retains duplicates C) the projection operation in relational algebra D) the projection operation in relational algebra, except that SELECT in SQL retains duplicates

Official answer: D) the projection operation in relational algebra, except that SELECT in SQL retains duplicates. Explanation: In relational algebra, the projection operation ( ) selects specific attributes (columns) from a relation and eliminates duplicate tuples by default (as relations are mathematical sets). In SQL, the `SELECT` clause specifies the list of attributes to project. However, SQL operates on multiset (bag) semantics, so `SELECT` retains duplicate rows unless explicitly told to eliminate them using `SELECT DISTINCT`. Therefore, the SQL `SELECT` operation corresponds to the projection operation in relational algebra, except that `SELECT` in SQL retains duplicates. Hence, (D) is the correct option.

A) the selection operation in relational algebra

B) the selection operation in relational algebra, except that SELECT in SQL retains duplicates

C) the projection operation in relational algebra

D) the projection operation in relational algebra, except that SELECT in SQL retains duplicates

Databases · SQL

Official IIT answer key · IIT Kanpur · Audited Aug 2026

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GATE CSE 2015 Set 1 Q7 · MCQ · 1 mark

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In GATE CS, SQL is tested through a balanced mix of declarative query semantics, relational-algebra correspondence, subquery evaluation (correlated, nested, and universal quantification), and instance-level tracing. Questions range from conceptual integrity rules (DDL constraints, FOREIGN KEY targets, GROUP BY/HAVING rules) to practical computation of output row counts and aggregate values on small database instances. Recent papers strongly emphasize NAT execution traces and multi-correct (MSQ) equivalent query formulations.

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Databases · SQL

Official IIT answer key · IIT Kanpur · Audited Aug 2026

Take topic test

GATE CSE 2015 Set 1 Q7 · MCQ · 1 mark

SELECT operation in SQL is equivalent to

Select an option to check

Key concept

SQL

Step-by-step verified solution

Examiner trap & misconception

Topic notes

How GATE tests SQL

Full SQL guide →

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All 17 questions on SQL →

Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.

SELECT operation in SQL is equivalent to

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SELECT operation in SQL is equivalent to

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SELECT operation in SQL is equivalent to

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SELECT operation in SQL is equivalent to

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