Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?

From: paul c <toledobythesea_at_dbms.yuc>
Date: Thu, 02 Nov 2006 03:42:17 GMT
Message-ID: <tOd2h.237313$5R2.133420@pd7urf3no>

Brian Selzer wrote:
> "paul c" <toledobythesea_at_dbms.yuc> wrote in message
> news:pic2h.242958$R63.119230_at_pd7urf1no...

>> Brian Selzer wrote:
>>> <saturnlee_at_yahoo.com> wrote in message 
>>> news:1162158876.794350.29460_at_f16g2000cwb.googlegroups.com...
>>>> I have a basic question.
>>>> Suppose there are 3 attributes: A,B and C.
>>>> And there are no FD(trivial and non trivial )
>>>>
>>>> What 's the key for it? ABC or nothing???
>>>>
>>> A relation with at least one attribute *ALWAYS* has at least one FD. 
>>> Here are some of them for your example:
>>>
>>> {ABC} --> A
>>> {ABC} --> B
>>> {ABC} --> C
>>> {ABC} --> {ABC}
>>>
>>> Note that all of the FD's are trivial.
>>>
>>>
>> Wouldn't a relation with no attributes also have a trivial FD?
>>

>
> I'm not sure: I've never thought about it. Is {} --> {} trivial? Probably
> so.

Alright, I'll risk displaying my ignorance and ask if such a relation has exactly one FD, is there a way to count to two? (and thus three, four ...)

p Received on Wed Nov 01 2006 - 21:42:17 CST