Re: PG won't use index on ORDER BY <expression>

On Thursday 09 August 2007 22:00:54 Gregory Stark wrote:
> "Andreas Joseph Krogh" <andreak(at)officenet(dot)no> writes:
> > I create an index:
> > CREATE INDEX person_lowerfullname_idx ON
> > person((lower(COALESCE(firstname, '')) || lower(COALESCE(lastname, '')))
> > varchar_pattern_ops);
>
> Why are you declaring it using the varchar_pattern_ops?
>
> The default operator set is the one you want for handling ordering. The
> pattern_ops operator set is for handling things like x LIKE 'foo%'

Ooops, just fugured that out. But - it still doesn't use the index if I remove
the "varchar_pattern_ops". I solved it by adding a function:

CREATE OR REPLACE FUNCTION concat_lower(varchar, varchar) RETURNS varchar AS
$$
SELECT lower(coalesce($1, '')) || lower(coalesce($2, ''))
$$ LANGUAGE SQL IMMUTABLE;

And than creating an index:
CREATE INDEX person_lowerfullname_idx ON person(concat_lower(firstname,
lastname));

Another question then: Why doesn't "varchar_pattern_ops" handle ordering? This
means I need 2 indexes on the columns I want to match with LIKE and ORDER BY.
Just doesn't seem right to need 2 "similar" indexes...

--
Andreas Joseph Krogh <andreak(at)officenet(dot)no>
Senior Software Developer / Manager
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