> -----Mensagem original----- > De: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general- > owner@xxxxxxxxxxxxxx] Em nome de Marti Raudsepp > Enviada em: segunda-feira, 26 de setembro de 2011 17:42 > Para: Edson Carlos Ericksson Richter > Cc: pgsql-general@xxxxxxxxxxxxxx > Assunto: Re: Does postgresql 9.0.4 use index on PREFIX%SUFFIX > queries? > > On Mon, Sep 26, 2011 at 15:16, Edson Carlos Ericksson Richter > <richter@xxxxxxxxxxxxxx> 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 > > -- > Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make > changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general
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