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Date: Tue, 28 Feb 2012 13:38:35 +0100
From: Richard Klingler <richard@klingler.net>
To: pgsql-sql@postgresql.org
Message-ID: <20120228133835204823.bbf29d1f@klingler.net>
In-Reply-To: 
 <CAP_rwwkrnuANFjirZvkS=Ca2gejQvQa-xnM-vXsOFSQ1Jy92cQ@mail.gmail.com>
References: <20111217113306531983.1eb85a86@klingler.net>
	<CAP_rwwkrnuANFjirZvkS=Ca2gejQvQa-xnM-vXsOFSQ1Jy92cQ@mail.gmail.com>
Subject: Re: Natural sort order
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Took some time until I could try out this...

But as soon I want to create the fcuntion based index it tells me:

=09Error : ERROR:  functions in index expression must be marked IMMUTABLE

Deleteing the sort function and recreating with the IMMUTABLE attribute giv=
es the same error..

Here the functions:

CREATE FUNCTION btrsort_nextunit(text) RETURNS text AS $$
=09SELECT=20
=09=09CASE WHEN $1 ~ '^[^0-9]+' THEN
=09=09=09COALESCE( SUBSTR( $1, LENGTH(SUBSTRING($1 FROM '[^0-9]+'))+1 ), ''=
 )
=09=09ELSE
=09=09=09COALESCE( SUBSTR( $1, LENGTH(SUBSTRING($1 FROM '[0-9]+'))+1 ), '' =
)
=09=09END

$$ LANGUAGE SQL
IMMUTABLE;

CREATE FUNCTION btrsort(text) RETURNS text AS $$
=09SELECT=20
=09=09CASE WHEN char_length($1)>0 THEN
=09=09=09CASE WHEN $1 ~ '^[^0-9]+' THEN
=09=09=09=09RPAD(SUBSTR(COALESCE(SUBSTRING($1 FROM '^[^0-9]+'), ''), 1, 12)=
, 12, ' ') || btrsort(btrsort_nextunit($1))
=09=09=09ELSE
=09=09=09=09LPAD(SUBSTR(COALESCE(SUBSTRING($1 FROM '^[0-9]+'), ''), 1, 12),=
 12, ' ') || btrsort(btrsort_nextunit($1))
=09=09=09END
=09=09ELSE
=09=09=09$1
=09=09END
      ;
$$ LANGUAGE SQL
IMMUTABLE;


And the index creation:

create index port_name_btrsort_index on port(btrsort(name));

Which should speed up my query:

=09select * from port where name not like '%Z' order by btrsort(name) asc



cheers
richard


On Sat, 17 Dec 2011 16:16:07 +0100, Filip Rembia=B3kowski wrote:
> If you use btrsort(column) from the example, you can just create a
> functional index on this expression.
>=20
> CREATE INDEX mytable_column_btrsort_idx ON mytable( btrsort(column) );
>=20
> this can help.
>=20
>=20
>=20
>=20
>=20
> 2011/12/17 Richard Klingler <richard@klingler.net>:
>> Morning...
>>=20
>> What is the fastest way to achieve natural ordering from queries?
>>=20
>> I found a function at:
>> http://2kan.tumblr.com/post/361326656/postgres-natural-ordering
>>=20
>> But it increases the query time from around 0.4msecs to 74msecs...
>> Might be not much if occasional queries are made..but I use it for
>> building
>> up a hierarchical tree menu in a web application where every msecs
>> counts (o;
>>=20
>>=20
>> cheers
>> richard
>>=20
>>=20
>> --
>> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
>> To make changes to your subscription:
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>=20
> --=20
> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
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