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Discussion :: GATE CSE

  1. 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?
    2. A.
    πB(r1) - πC(r2) = Ø
    B.
    πC(r2) - πB(r1) = Ø
    C.
    πB(r1) = πC(r2)
    D.
    πB(r1) - πC(r2) ≠ Ø

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    Answer : Option A

    Explanation :

    -NA-

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