Ace Test Series: DBMS - Functional Dependency

Question

 

Comments

$C\,?$

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Why not B ?

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They must agree if $t_1$ and $t_2$ are the same at $A$ if they don't then it doesn't matter what the value of $B$ is, two different can map to the same value and different.

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What does it mean by they both disagree does it mean that both tuples has different values ?

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Value of $a$ is different in both tuples, that's what i think

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Well Consider

       A            B

       2             X1

       4             X2

Now if u put any value in X it will always satisfy A -> B.

Becasue to violate it I should have two entries of A to be same pointing to different values of B like:

       A            B

       2             4

       2             3

Here A -> B doesn't exists

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That's exactly what the question asks i guess, what you explained in the first point so B may agree or disagree still the FD hold.

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ohk i got that thnks