RES: Does postgresql 9.0.4 use index on PREFIX%SUFFIX queries?

> -----Mensagem original-----
> De: pgsql-general-owner(at)postgresql(dot)org [mailto:pgsql-general-
> owner(at)postgresql(dot)org] Em nome de Marti Raudsepp
> Enviada em: segunda-feira, 26 de setembro de 2011 17:42
> Para: Edson Carlos Ericksson Richter
> Cc: pgsql-general(at)postgresql(dot)org
> 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
> <richter(at)simkorp(dot)com(dot)br> 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);
>
> And then write your queries like this:
> SELECT * FROM foobar
> WHERE txt like 'POA%34345'
> AND reverse(txt) like reverse('POA%34345');

Just perfect! It not only works, but time dropped from 5s to 94ms.

Regards,

Edson.

>
> PostgreSQL will automatically choose one or both indexes for executing
> this query.
>
> Regards,
> Marti
>
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