GATE-2012 -43 Foreign key Dependency

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:-

A.    \prod_{B}(r_{1})- \prod _{C}(r_{2})= \varnothing

 

B.    \prod_{C}(r_{2})- \prod _{B}(r_{1})= \varnothing

 

C.    \prod_{B}(r_{1}) = \prod _{C}(r_{2})

 

D.    \prod_{B}(r_{1}) - \prod _{C}(r_{2}) \neq \varnothing

Answer

now, you take each example and try to get the corresponding output.

Referential Integrity means each and every value in foreign key must be present in the parent attribute but the reverse is not compulsory true.

 

Option B:  c4 will be there So FALSE.

Option C: Nope. false

Option D:- False.

Option A:  True

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