Re: 4 the FAQ: Are Commercial DBMS Truly Relational?

"Laconic2" <laconic2_at_comcast.net> wrote in message news:ur6dnYyKodQZNvXcRVn-ow_at_comcast.com...
>
> "Marshall Spight" <mspight_at_dnai.com> wrote in message
> news:eP%9d.219935$D%.37995_at_attbi_s51...
> > However, note that the result of an outer join is not necessarily a
> > > relation, even if both of the operands are relations.
> >
> > You lost me. Do you mean something besides the part where
> > there are no rows on the right corresponding to rows on the
> > left, or do you mean something else?
>
> No. I meant that an outer join can introduce NULLS, and NULLS don't belong
> in relations.

Right, but although you certainly need an operation like this, SQL's outer join is not the only way to get it. I rather think that GROUP/UNGROUP, and result columns of relation type, are a better approach, in part because NULLs are not required.

> I hope I'm not being too dogmatic about this.

Not at all.

Marshall Received on Sun Oct 10 2004 - 05:55:36 CEST