Re: PG won't use index on ORDER BY

On Thursday 09 August 2007 22:57:35 Rodrigo De León wrote:
> On 8/9/07, Andreas Joseph Krogh <andreak@officenet.no> wrote:
> > Ooops, just fugured that out. But - it still doesn't use the index if I
> > remove the "varchar_pattern_ops".
>
> Huh?
>
> CREATE INDEX person_lowerfullname_idx
> ON person
> ((lower(COALESCE(firstname, '')) || lower(COALESCE(lastname, ''))));
>
>
> EXPLAIN ANALYZE select id from person order by
> (lower(COALESCE(firstname, '')) ||
> lower(COALESCE(lastname, ''))) ASC limit 1;
>
> Limit  (cost=0.00..0.08 rows=1 width=68) (actual time=0.030..0.030
> rows=0 loops=1)
>   ->  Index Scan using person_lowerfullname_idx on person
> (cost=0.00..62.25 rows=800 width=68) (actual time=0.018..0.018 rows=0
> loops=1)
> Total runtime: 0.318 ms
>
>
> EXPLAIN ANALYZE select id from person
> where (lower(COALESCE(firstname, '')) ||
> lower(COALESCE(lastname, ''))) like 'A%'
> order by (lower(COALESCE(firstname, '')) || lower(COALESCE(lastname, '')))
> ASC limit 1;
>
> Limit  (cost=0.01..5.10 rows=1 width=68) (actual time=0.038..0.038
> rows=0 loops=1)
>   ->  Index Scan using person_lowerfullname_idx on person
> (cost=0.01..20.34 rows=4 width=68) (actual time=0.032..0.032 rows=0
> loops=1)
>         Index Cond: (((lower((COALESCE(firstname, ''::character
> varying))::text) || lower((COALESCE(lastname, ''::character
> varying))::text)) >= 'A'::text) AND ((lower((COALESCE(firstname,
> ''::character varying))::text) || lower((COALESCE(lastname,
> ''::character varying))::text)) < 'B'::text))
>         Filter: ((lower((COALESCE(firstname, ''::character
> varying))::text) || lower((COALESCE(lastname, ''::character
> varying))::text)) ~~ 'A%'::text)
> Total runtime: 0.138 ms
>
>
> Works for me.

I forgot to mention: I use UTF-8. IIRC, it works fine with C-locale without
the "varchar_pattern_ops", which is why it works for you I think.

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
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