Re: Design question regarding data typing

"Bob Hairgrove" <invalid_at_bigfoot.com> wrote in message news:2phuv15e4149insj1a9ia3m2fdbsfm04ml_at_4ax.com...
> On 24 Feb 2006 09:39:43 -0800, "Jacob JKW" <jacobcdf_at_yahoo.com> wrote:
>
> >Sure. I was trying to explain that one column of my Insitutions table
> >was the foreign key InstitutionTypeId which indexes the name (and
> >description) of the type of institution (which in this simplification
> >can be either "school" or "bank"). I have this in addition to separate
> >Banks and Schools tables. The reason for using the InstitutionType
> >descriptor (or as I gather it's called from Roy's post above,
> >"discriminant") is so that if I want summary instituition data from
> >Insitutions I can easily figure out the institution type without having
> >to scan for each InstutionId foreign key of interest in Banks Schools.
> >And that's the kludge that's causing me such consternation. :-( It just
> >reeks of bad form.
>
> Yes, InstitutionTypeId is redundant data if you already have separate
> tables as described. I don't see the need for it unless for some
> reason you want to avoid the join or subquery which would be necessary
> without it should you want to group or sort by schools or banks. A
> simple natural join of two tables on their primary key columns is
> going to perform very fast in every RDBMS that I know of ... you'll
> never have to do a full table scan for that.

Agreed. Also, lest Jacob should confuse his colleagues with that snappy new buzzword (discriminator), I didn't even notice I'd used it. I suspect that bobbed up (like a putrid corpse from the swamp) from some ancient Algol text I may once have read.

Roy Received on Fri Feb 24 2006 - 19:09:18 CET