Message-ID: <445CA989.60308@logix-tt.com>
Date: Sat, 06 May 2006 15:50:01 +0200
From: Markus Schaber <schabi@logix-tt.com>
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To: =?ISO-8859-2?Q?Miroslav_=A9ulc?= <miroslav.sulc@startnet.cz>
CC: pgsql-sql@postgresql.org
Subject: Re: Most efficient way to hard-sort records
References: <445C5A94.4020907@startnet.cz>
In-Reply-To: <445C5A94.4020907@startnet.cz>
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Hi, Miroslav,

Miroslav Šulc schrieb:

> I have a table with cca 100,000 records. I need to hard-sort the records
> by a key from second table. By hard-sorting I mean storing position of
> each row in the main table. Here is what my tables look like:
> 
> main_table: id, name, position
> key_table: id, main_table_id, key, value
> 
> Here is how I need to sort the records:
> SELECT * FROM main_table
> INNER JOIN key_table ON main_table.id = key_table.main_table_id
> WHERE key = 'param'
> ORDER BY value
> 
> I currently collect all ids from main_table in sorted order and then
> update the position field for each row in the main_table one-by-one. Is
> there a better/faster/more efficient solution?

Create an SQL function that selects the sort value from the key table
when given id as parameter, and then create a functional index on the
table, and CLUSTER the table on the index.

Scratch-Code (untested):

CREATE FUNCTION getvalue (ID int4) RETURNS int4 AS
" SELECT value FROM key_table WHERE value=$1 LIMIT 1"
LANGUAGE SQL STRICT;

CREATE INDEX main_table_order_idx ON main_table (getvalue(id));

CLUSTER main_table_order_idx ON main_table;


HTH,
Markus