Re: Lucid statement of the MV vs RM position?
From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Fri, 05 May 2006 08:30:48 +0200
Message-ID: <e3eren$fd0$1_at_orkan.itea.ntnu.no>
>
> Maybe I should have said that group always seems to imply an additional
> FD in the result and ungroup always seems to imply the removal of one in
> the result?
Date: Fri, 05 May 2006 08:30:48 +0200
Message-ID: <e3eren$fd0$1_at_orkan.itea.ntnu.no>
paul c wrote:
> Jon Heggland wrote:
>> paul c wrote: >>> (group and ungroup seem to always imply a key, possibly a >>> different one from the input relvar's key and this seemed a little >>> chicken and egg to me). >> >> I don't understand this.
>
> Maybe I should have said that group always seems to imply an additional
> FD in the result and ungroup always seems to imply the removal of one in
> the result?
Yes, now I see what you mean. Certainly the output of a relational operation will have different FDs/keys than the input. That is to be expected---the set of attributes changes, after all---and it goes for *all* the relational operators, not just group/ungroup. What's chicken/egg about it?
-- JonReceived on Fri May 05 2006 - 08:30:48 CEST