Re: immutable functions vs. join for lookups ?

On 4/17/05, Enrico Weigelt <weigelt@metux.de> wrote:
> * Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > Enrico Weigelt <weigelt@metux.de> writes:
> > > c) CREATE FUNCTION id2username(oid) RETURNS text
> > >     LANGUAGE 'SQL' IMMUTABLE AS '
> > >     SELECT username AS RESULT FROM users WHERE uid = $1';
> >
> > This is simply dangerous.  The function is *NOT* immutable (it is
> > stable though).  When ... not if ... your application breaks because
> > you got the wrong answers, you'll get no sympathy from anyone.
>
> In my case it is immutable. The username never changes.
>
Even if your data never changes it *can* change so the function should
be at most stable not immutable.

regards,
Jaime Casanova