Re: index on to_char(created, 'YYYY') doesn't work

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On Wednesday 15 January 2003 16:12, you wrote:
> On Wed, 15 Jan 2003, Andreas Joseph Krogh wrote:
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> > On Wednesday 15 January 2003 11:37, you wrote:
> > > The following does not work:
> > >
> > > create index session_u_idx on session (to_char(created, 'YYYY'));
> > > ERROR: parser: parse error at or near "'YYYY'" at character 57
> > >
> > > Can I make a function to do this and index using the result of that
> > > funtion? Do anyone have an example of such a function?
> >
> > I tried the following function:
> > - -----------------------------------------------------------------
> > create function drus (timestamp) returns varchar AS'
> > DECLARE
> > str_created VARCHAR;
> > created ALIAS FOR $1;
> > BEGIN
> > str_created:= to_char(created, ''YYYY'');
> > RETURN str_created;
> > END;
> > ' LANGUAGE 'plpgsql';
>
> add
> WITH (iscachable)

Thank you, not _that_ works:-)
But now this doesn't work:
create index session_u_idx on session (drus(created), username);

Can't I have multicolumn-indexes with functions? Any idea how to rewrite that
so it works?
Here is my session table:
CREATE TABLE session (
session_id varchar(256) NOT NULL PRIMARY KEY,
created timestamp DEFAULT 'now' NOT NULL,
last_accessed timestamp NOT NULL,
destroyed timestamp NOT NULL,
username varchar -- Allow sessions from not logged in users
);

Here is my query I wish to optimize using indexes:
SELECT to_char(created, 'IW') as week, count(session_id) from session WHERE
username IS NULL and to_char(created, 'YYYY') = '2002' group by week ORDER BY
week;

Any hints on optimizing this query, index-usage etc?

- --
Andreas Joseph Krogh <andreak(at)officenet(dot)no>
There will always be someone who agrees with you
but is, inexplicably, a moron.

gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
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