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 Functional dependencies
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SQLapprentice
Starting Member

29 Posts

Posted - 01/09/2013 :  11:29:20  Show Profile  Reply with Quote
Hi all,

How do functional dependencies Help make a better relational database and how can we assure simple functional dependencies to be complied?

Lamprey
Flowing Fount of Yak Knowledge

4613 Posts

Posted - 01/09/2013 :  12:52:05  Show Profile  Reply with Quote
It has to do with the lossless-join decomposition property. Here is a link to a wiki about the subject that does a decent job of describing things:
http://en.wikipedia.org/wiki/Functional_dependency

If you are interested in these things and you haven't already, I'd highly suggest you read An Introduction To Database Systems by CJ Date (http://books.google.com/books/about/An_Introduction_To_Database_Systems_8_E.html?id=EFUn2u6klHkC)
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Jeff Moden
Aged Yak Warrior

USA
649 Posts

Posted - 01/09/2013 :  21:18:58  Show Profile  Reply with Quote
In English, it makes sure that people can't enter garbage in the database nor can they make certain deletes that would leave orphans. As you can imagine, there's more to it than that but those are the two most important things that come to mind.

--Jeff Moden
RBAR is pronounced "ree-bar" and is a "Modenism" for "Row By Agonizing Row".

First step towards the paradigm shift of writing Set Based code:
"Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

When writing schedules, keep the following in mind:
"If you want it real bad, that's the way you'll likely get it."
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