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 01:42:30 GMT
Message-ID: <a2c2h.242940$R63.209531_at_pd7urf1no>
>
>
> ABC is not the key.
> Example: Let one partricular entity has A,B,C atributes
> and let these atributes take the following values:
>
> A B C
> -----------------------------
> 2 4 6
> 8 4 6
> 2 4 6
>
> ( ABC can be the key only in the trivial cases i.e if an entity has
> the atributes whose values never change)
>
Date: Thu, 02 Nov 2006 01:42:30 GMT
Message-ID: <a2c2h.242940$R63.209531_at_pd7urf1no>
vldm10 wrote:
> saturnlee_at_yahoo.com wrote:
>> What 's the key for it? ABC or nothing???
>
>
> ABC is not the key.
> Example: Let one partricular entity has A,B,C atributes
> and let these atributes take the following values:
>
> A B C
> -----------------------------
> 2 4 6
> 8 4 6
> 2 4 6
>
> ( ABC can be the key only in the trivial cases i.e if an entity has
> the atributes whose values never change)
>
There are more precise writers than I here but since they haven't commented:
- Are you talking about SQL? If so, I think you should have said so because ABC is certainly a candidate key if the above table is a relation and no subset of {A,B,C} is stipulated as a key.
- I don't know why entities need to be mentioned, either, nor what a non-"trivial" entity might possibly be.
p Received on Thu Nov 02 2006 - 02:42:30 CET