Database-Management-System
August 29, 2024Database-Management-System
August 29, 2024Database-Management-System
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Question 281
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Suppose (A, B) and (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?
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πC(r2) – πB(r1) = Ф
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πB(r1) -πC(r2) = Ф
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πB(r1) – πC(r2) ≠ Ф
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πB(r1) – πC(r2) = Ф
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Question 281 Explanation:
Since B is the foreign key that refers C in r2. So the B will contain the values that will be definitely present in C and C might contain more different values. So for sure
πB(r1) -πC(r2) = Ф
πB(r1) -πC(r2) = Ф
Correct Answer: B
Question 281 Explanation:
Since B is the foreign key that refers C in r2. So the B will contain the values that will be definitely present in C and C might contain more different values. So for sure
πB(r1) -πC(r2) = Ф
πB(r1) -πC(r2) = Ф
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