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: What databases have taught me

Re: What databases have taught me

From: Marshall <marshall.spight_at_gmail.com>
Date: 23 Jun 2006 18:55:30 -0700
Message-ID: <1151114130.829529.240780@p79g2000cwp.googlegroups.com>


Bob Badour wrote:
>
> Consider:
>
> Ra = Rb AND x = 1 AND y = 1
>
> Where Ra and Rb are two relvars. Is that still a join? To what do x and
> y refer?
>
> Consider:
>
> R AND x = 1 AND y = 1
>
> where R has no x attribute. Will that cause a compile-time error? Why or
> why not?

I may be short on context here; is this being asked against a specific language (rel?) Because the answer will depends on the language, of course.

At least for the second question, I'd expect that it wouldn't be a compile time error, because AND is natural join, and natural join has well-defined semantics when the two relations have no attributes in common. (Cartesian product.)

Marshall Received on Fri Jun 23 2006 - 20:55:30 CDT

Original text of this message

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