Subject: RES: [GENERAL] Does postgresql 9.0.4 use index on PREFIX%SUFFIX queries?
From: "Edson Carlos Ericksson Richter" <[email-masked]>
To: <[email-masked]>
Date: Mon, 26 Sep 2011 19:43:50 -0300
List-Id: <pgsql-general.postgresql.org>

> -----Mensagem original-----
> De: [email-masked] [mailto:pgsql-general-
> [email-masked]] Em nome de Marti Raudsepp
> Enviada em: segunda-feira, 26 de setembro de 2011 17:42
> Para: Edson Carlos Ericksson Richter
> Cc: [email-masked]
> Assunto: Re: [GENERAL] Does postgresql 9.0.4 use index on PREFIX%SUFFIX
> queries?
> 
> On Mon, Sep 26, 2011 at 15:16, Edson Carlos Ericksson Richter
> <[email-masked]> wrote:
> > select * from notafiscal where numeroctc like ‘POA%34345’;
> >
> > Prefix is normally 3 characters, suffix varyies.
> >
> > Is Postgresql 9.0.4 able to use an BTREE index on notafiscal.numeroctc
> to execute this query?
> 
> As mentioned by other posters, you should use a btree index with
> text_pattern_ops opclass to speed up this query.
> 
> For queries like these, it's often faster to match the text in *reverse*.
> You can create two indexes like this:
> 
> create index on foobar (txt text_pattern_ops); create index on foobar
> (reverse(txt) text_pattern_ops);

I got the following error:

ERROR: function reverse(text) does not exist
SQL state: 42883
Hint: No function matches the given name and argument types. You might need to add explicit type casts.
Character: 29

> 
> And then write your queries like this:
> SELECT * FROM foobar
> WHERE txt like 'POA%34345'
>   AND reverse(txt) like reverse('POA%34345');
> 
> PostgreSQL will automatically choose one or both indexes for executing
> this query.
> 
> Regards,
> Marti
> 
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