Re: Null values in indexes

> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: Wednesday, May 29, 2002 9:07 AM
> To: Jan Wieck
> Cc: Oleg Bartunov; Teodor Sigaev; pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] Null values in indexes
>
>
> Jan Wieck <janwieck@yahoo.com> writes:
> > Tom Lane wrote:
> >> Hannu Krosing <hannu@tm.ee> writes:
> > How hard would it be to _not_ include nulls in indexes
> > as they are not used anyway.
> >>
> >> Seems to me that would be a step backwards.
>
> >     It  would cause multi-key indexes beeing unusable for partial
> >     key lookup. Imagine you have a key over (a, b, c)  and  query
> >     with  WHERE  a = 1 AND b = 2. This query cannot use the index
> >     if a NULL value in c  would  cause  the  index  entry  to  be
> >     suppressed.
>
> Urgh ... that means GiST indexing is actually broken, because GiST
> currently handles multicolumns but not nulls.  AFAIR the planner
> will try to use partial qualification on any multicolumn index...
> it had better avoid doing so for non-null-capable AMs.
>
> Alternatively, we could fix GiST to support nulls.  Oleg, Teodor:
> how far away might that be?

The PostGIS people have already fixed it.  However, they may not be
willing to contribute the patch.  On the other hand, I think it would be
in their interest, since the source code trees will fork if they don't
and they will have trouble staying in synch with PostgreSQL
developments.  (See the 7.2 index project here:
http://postgis.refractions.net/
http://postgis.refractions.net/news/index.php?file=20020425.data
)

If they are not willing to commit a patch, I suspect that they will at
least tell you what they had to do to fix it and it could be performed
internally.