Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: No exceptions?

Re: No exceptions?

From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Fri, 30 Jun 2006 09:58:55 +0200
Message-ID: <e82lnp$k12$1@orkan.itea.ntnu.no>


Bob Badour wrote:
> The extend operation creates a new relation by adding an attribute to an
> existing one. Strictly speaking, whether the candidate key would be
> preserved depends on the operation used to derive the extended
> attributes. Ungrouping a relation valued attribute, for instance, would
> affect the key. However, most familiar extend operations would not.

I think it is a bit misleading to consider ungroup an example of extend. For one thing: The extend operator as normally defined does not affect cardinality; ungroup does (in general).

-- 
Jon
Received on Fri Jun 30 2006 - 02:58:55 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US