Question 3142 – Research Aptitude
April 21, 2024Question 4575 – Higher-Education-and-Politics
April 22, 2024Question 8847 – Database-Management-System
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?
Correct Answer: A
Question 23 Explanation:
Referential integrity means, all the values in foreign key should be present in primary key.
So we can say that r2(C) is the superset of r1(B).
So (subset – superset) is always empty.
So we can say that r2(C) is the superset of r1(B).
So (subset – superset) is always empty.
∏B (r1) – ∏C (r2) = ∅
∏C (r2) – ∏B (r1) = ∅
∏B (r1) = ∏C (r2)
∏B (r1) – ∏C (r2) ≠ ∅
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