Re: why is index not used?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Marcin Krol <mrkafk(at)gmail(dot)com>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: why is index not used?
Date: 2008-10-28 16:14:15
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Marcin Krol <mrkafk(at)gmail(dot)com> writes:
> booktown=# explain analyze select * from auth where first_name like 'a11%';
> --------------------------------------------------------------------------------------------------------
> Seq Scan on auth (cost=0.00..56796.68 rows=1 width=42) (actual
> time=0.091..983.665 rows=1111 loops=1)
> Filter: ((first_name)::text ~~ 'a11%'::text)
> Total runtime: 986.314 ms
> (3 rows)

> FAQ says that in order to use index, LIKE statements cannot begin with
> %, so I should be fine?

The other point is that in non-C locales, a standard varchar index isn't
usable for LIKE (the sort order is usually wrong). You can re-initdb
in C locale or create a varchar_pattern_ops index.

regards, tom lane

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