Suppose R 1 (A, B) and R 2 (C, D) are two relation schemas. Let r 1 and r 2 be the corresponding relation instances. B is a foreign key that refers to C in R 2 . If data in r 1 and r 2 satisfy referential integrity constraints, which of the following is ALWAYS TRUE ?

Correct Answer is : ΠB(r1) - ΠC(r2) = Φ

GATE Computer Science (CS) 2012 Solved Paper

Question : 53 of 65

Marks: +1, -0

Suppose R₁(A, B) and R₂(C, D) are two relation schemas. Let r₁ and r₂ be the corresponding relation instances. B is a foreign key that refers to C in R₂. If data in r₁ and r₂ satisfy referential integrity constraints, which of the following is ALWAYS TRUE?

Π_B(r₁) - Π_C(r₂) = Φ
Π_C(r2) - ΠB(r1) = Φ
ΠB(r1) = ΠC(r2)
ΠB(r1) - ΠC(r2) ≠ Φ

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