GATE | GATE-CS-2001 | Question 25

Let r and s be two relations over the relation schemes R and S respectively, and let A be an attribute in R. then the relational algebra expression is always equal to

(A) A
(B) B
(C) C
(D) D

Answer: (C)
Explanation: The above expression evaluates A = a for tables r and s

Option A : is only displaying attributes of table r on the select condition

Option B : is only displaying attributes of table r

Option C: evaluates A = a by joining tables r and s  efficiently , thus correct

Therefore, Answer C

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