Re: thinking about UPDATE

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:pan.2004.07.23.08.58.40.657256_at_REMOVETHIS.pandora.be...
> On Fri, 23 Jul 2004 08:08:32 +0000, Dan wrote:
>
> FDs of the form {}->Y are very strong statements and therefore rarely
> true. If it would hold that {}->{QTY} then there can be at most one value
> in the QTY column. If it would hold that {}->{P#} then there can be at
> most one value in the P# column. Since {}->{P#,QTY} is essentially the
> conjunction of the previous two, that's an even stronger statement:
> every shipment contains the same part in the same quantity.
>
> Note that in practice you would probably not include such columns because
> they are obviously redundant. Actually, theory says the same because the
> relation would not be in 3NF (or even 2NF).
>
> -- Jan Hidders
>
Thank you again. This might be old hat for you and Mikito, but this is an eye-opener for me. I never thought about this particular case when dealing with FD's. Much appreciation to you both for your patience. Received on Fri Jul 23 2004 - 11:07:55 CEST