Re: create index with substr function

As previously suggested by Stephan Szabo, you need to create a helper
function, e.g.:
create or replace function after9(text)returns text language plpgsql immutable as '
   begin
   return substr($1, 10);
   end;
';

You may need the "immutable" specification is to allow the
function's use in an index.

Then use this function in the index creation:

CREATE INDEX idx_doc_substr_doc_urn ON doc USING btree (after9(doc_urn));

I think that should do it.


-- George
>
On Thu, 21 Oct 2004 11:37:26 +0800
"Ray" <ray_siu@ge-ts.com.hk> threw this fish to the penguins:

> sorry it doesn't works, as my postgres is 7.3 not 7.4. any other alternative
> solution for version after 7.4??
>
> Thank
> Ray : )
>
> ----- Original Message -----
> From: "Rosser Schwarz" <rosser.schwarz@gmail.com>
> To: "Ray" <ray_siu@ge-ts.com.hk>
> Cc: <pgsql-performance@postgresql.org>
> Sent: Thursday, October 21, 2004 11:34 AM
> Subject: Re: [PERFORM] create index with substr function
>
>
> > while you weren't looking, Ray wrote:
> >
> > > CREATE INDEX idx_doc_substr_doc_urn ON doc USING btree
> (SUBSTR(doc_urn,10));
> >
> > CREATE INDEX idx_doc_substr_doc_urn ON doc USING btree
> ((SUBSTR(doc_urn,10)));
> >
> > You need an additional set of parens around the SUBSTR() call.
> >
> > /rls
> >
> > --
> > :wq
> >
>
>
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