Re: Functional Dependencies?
From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 02 Oct 2005 23:22:43 GMT
Message-ID: <7ZZ%e.58734$tl2.33476_at_pd7tw3no>
>
>
> Yes. Which, as others have said, indicates that there is at most one
> row in the relation - and, further, that there are no other FDs because
> any other FD necessarily has the empty set as a subset of the LHS
> (determinant) of the putative FD.
>
>
>
> Not really; it is a trivial FD since the RHS is a subset of the LHS of
> the FD.
>
Date: Sun, 02 Oct 2005 23:22:43 GMT
Message-ID: <7ZZ%e.58734$tl2.33476_at_pd7tw3no>
Jonathan Leffler wrote:
> paul c wrote:
>
>> I presume this is the same as saying that the attribute set, {}, is a
>> key.
>
>
> Yes. Which, as others have said, indicates that there is at most one
> row in the relation - and, further, that there are no other FDs because
> any other FD necessarily has the empty set as a subset of the LHS
> (determinant) of the putative FD.
>
>> I wonder if the FD {X} -> {} means anything?
>
>
> Not really; it is a trivial FD since the RHS is a subset of the LHS of
> the FD.
>
thanks Jonathan - i owe you two now.
pc Received on Mon Oct 03 2005 - 01:22:43 CEST