Functional Dependency

Question

R 

A	B
1	2
3	4
5	5
	5
	8

S

A	B
1	2
3	2
4	4
Null	5
Null	6
6	9

Can we say that A-> B in R and S?

Answer 1

****yes,we can say A->B in both R and S *****
because A->B means the attribute B contain some value which is unique for every value of A, that means B does not contain two value for 1 unique value of a.

Comments

@ AnilGoudar this is the given DB table.Its not particular instance

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@Rahul,

If that is the case, then we can sure about FD's  unless no additional tuples are added to table.

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But what about Nulls and empty records?