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BUG #4224: issue with LIMIT and ORDER BY

From: "Lawrence Cohan" <lawrencec(at)1shoppingcart(dot)com>
To: pgsql-bugs(at)postgresql(dot)org
Subject: BUG #4224: issue with LIMIT and ORDER BY
Date: 2008-06-05 18:15:29
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
The following bug has been logged online:

Bug reference:      4224
Logged by:          Lawrence Cohan
Email address:      lawrencec(at)1shoppingcart(dot)com
PostgreSQL version: 8.2.5
Operating system:   red hat 4.1.1-52
Description:        issue with LIMIT and ORDER BY

Following queries run FOREVER in PG if an index exists on the "id" column
which is a integer - serial and PKey on the table. 

SELECT id FROM orders WHERE merchant_id = xxxxxx ORDER BY id DESC LIMIT 31
-- or 30, 29, 28, 27, 26, 25


SELECT id FROM clients WHERE merchant_id = XXXXXX ORDER BY id LIMIT 3 -- or
1, 2.

With different limits we get different results but  the queris are running
forever with DESC as well. 
This is a serrios issue as PG documentation says that:

"When using LIMIT, it is important to use an ORDER BY clause that constrains
the result rows into a unique order. Otherwise you will get an unpredictable
subset of the query's rows. You might be asking for the tenth through
twentieth rows, but tenth through twentieth in what ordering?"


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Next:From: hubert depesz lubaczewskiDate: 2008-06-05 18:41:27
Subject: Re: BUG #4224: issue with LIMIT and ORDER BY
Previous:From: Simon RiggsDate: 2008-06-05 17:28:26
Subject: Re: BUG #3110: Online Backup introduces Duplicate OIDs

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