To: Theo Galanakis <Theo.Galanakis@lonelyplanet.com.au>
Cc: "'Josh Berkus'" <josh@agliodbs.com>, pgsql-sql@postgresql.org
Subject: Re: Isnumeric function?
References: <82E30406384FFB44AFD1012BAB230B55037D0591@shiva.au.lpint.net>
In-Reply-To: <82E30406384FFB44AFD1012BAB230B55037D0591@shiva.au.lpint.net>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 10 Sep 2004 02:43:46 -0400
Message-ID: <871xhatyhp.fsf@stark.xeocode.com>
Lines: 43
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii


Theo Galanakis <Theo.Galanakis@lonelyplanet.com.au> writes:

> I created the Index you specified, however it chooses to run a seq scan on
> the column rather than a Index scan. How can you force it to use that
> Index..
> 
> CREATE INDEX idx_content_numeric ON botched_table(content) WHERE content ~
> '^[0-9]{1,9}$';
> 
> select * from botched_table where content = 200::integer

You need to put a "and content ~ '^[0-9]{1,9}$'" in your query, the clause has
to match the clause in the partial index pretty closely.

perhaps you would find it convenient to make a view of
 select * from botched_table where content ~ '^[0-9]{1,9}$'
and then just always select these values from that view.

Also the "::integer" is useless. It actually gets cast to text here anyways.
The index is on the text contents of the content column.

You might consider making the index a functional index on content::integer
instead. I suspect that would be faster and smaller than an index on the text
version of content:

slo=> create table botched_table (content text);
CREATE TABLE
slo=> create index idx_botched_table on botched_table ((content::integer)) where content ~ '^[0-9]{1,9}$';
CREATE INDEX
slo=> create view botched_view as (select content::integer as content_id, * from botched_table where content ~ '^[0-9]{1,9}$');
CREATE VIEW
slo=> explain select * from botched_view where content_id = 1;
                                       QUERY PLAN                                       
----------------------------------------------------------------------------------------
 Index Scan using idx_botched_table on botched_table  (cost=0.00..3.72 rows=3 width=32)
   Index Cond: ((content)::integer = 1)
   Filter: (content ~ '^[0-9]{1,9}$'::text)
(3 rows)


-- 
greg