CODEWITHSUNDEEP
databasefunctional-dependencies
MUST_DIE
MUST_DIE

Reputation: 49

Determine functional dependicies

picture

possible answers:

A->B
C->D
A->C
C->A
B->C

I think only

A->B
A->C

are correct?

Upvotes: 0

Views: 45

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476659

Short answer: A -> B and A -> C are the only possible functional dependencies.

Well a functional dependency X -> Y means that if for two rows the X values are the same, then the Y values should be the same as well.

For A -> B that holds: the only value that is duplicated is a2. In both cases it maps to b3.

C -> D cannot be a functional dependency, because for c3, there are different d's.

When we analyze A -> C, we see that this is a potential functional dependency, because the only value in A that occurs twice (a2) again maps on the same value in the C column.

C -> A on the other hand is not a functional dependency. The value c3 occurs two times and maps to a1 and a5.

Finally B -> C also can't be a functional dependency: b1 maps to both c1 and c4.

Upvotes: 1

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