Re: Feature Proposal: Constant Values in Columns or Foreign Keys

Tom Lane wrote:

> =?UTF-8?Q?Nils_G=C3=B6sche?= <cartan@cartan.de> writes:

> > I was quite surprised to find that this wasn't possible. Is there any
> > good reason why not?
>
> It's contrary to SQL standard is why not.  And it's not just a matter
> of
> being outside the spec, as inheritance is; this is messing with the
> details of something that is defined in the standard.  As an example,
> I would wonder how such an FK is supposed to be represented in the
> spec-defined information schema views.  Other interesting questions
> include what would happen to the supposed constant during actions such
> as ON DELETE SET NULL or ON UPDATE CASCADE, which normally would result
> in a change in the referencing row.

Well, something I can have already is a column together with a NOT NULL constraint, and a CHECK constraint that ensures
thatthe value is really constant, and a foreign key that includes this constant column. You could just handle it the
sameway. 

The information schema is a good point, though. If the only way to put this into the information schema is to introduce
somedummy column, possibly with NULL as a name or something, then I don't like the idea much myself anymore. 

I guess the best I could hope for, then, is an optimization that does not store constant columns on disk ;-)

Regards,
--
Nils Gösche
"Don't ask for whom the <CTRL-G> tolls."