Question

Consider the following legal instance of a database:

A	B	C	D	E
‘a’	11	3	‘XY’	123
‘aa’	11	7	‘XY’	234
‘abc’	22	15	‘XY’	345
‘a’	22	16	‘XY’	456

Can the following functional dependency hold?

A --> B

Answer 1

The logic behind functional dependency holding is that for a given Left Hand Side (LHS) value of an attribute (or set of attributes) of a functional dependency, there should be at most one Right Hand Side (RHS) value of an attribute (or set of attributes). Then we would say that the functional dependency holds on that relation.

In the given relation A --> B, we see that the attribute 'a' of A has two values '11' and '22' in B, so in this relation, functional dependency doesn't hold.

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