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Re: LIKE query on indexes

From: Brendan Duddridge <brendan(at)clickspace(dot)com>
To: Ibrahim Tekin <itekin(at)gmail(dot)com>
Cc: "Scott Marlowe" <smarlowe(at)g2switchworks(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: LIKE query on indexes
Date: 2006-02-22 15:48:43
Message-ID: 78873B6F-1572-467C-8F98-9715FC8AC4AC@clickspace.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

Can this technique work with case insensitive ILIKE?

It didn't seem to use the index when I used ILIKE instead of LIKE.

Thanks,

____________________________________________________________________
Brendan Duddridge | CTO | 403-277-5591 x24 |  brendan(at)clickspace(dot)com

ClickSpace Interactive Inc.
Suite L100, 239 - 10th Ave. SE
Calgary, AB  T2G 0V9

http://www.clickspace.com

On Feb 21, 2006, at 1:28 PM, Ibrahim Tekin wrote:

> this trick did the job.
> thanks.
>
> On 2/21/06, Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
> Scott Marlowe wrote:
> > On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > > hi,
> > > i have btree index on a text type field. i want see rows which  
> starts
> > > with certain characters on that field. so i write a query like  
> this:
> > >
> > > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > >
> > > since this condition is from start of the field, query planner  
> should
> > > use index to find such elements but explain command shows me it  
> will
> > > do a sequential scan.
> > >
> > > is this lack of a feature or i am wrong somewhere?
> >
> > This is an artifact of how PostgreSQL handles locales other than  
> ASCII.
> >
> > If you want such a query to use an index, you need to back up your
> > database, and re-initdb with --locale=C as an argument.
>
> ... or you can choose to create an index with the text_pattern_ops
> operator class, which would be used in a LIKE constraint regardless of
> locale.
>
> http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
>
> --
> Alvaro Herrera                                 http:// 
> www.CommandPrompt.com/
> The PostgreSQL Company - Command Prompt, Inc.
>

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