Subject: Re: [SQL] OFFSET impact on Performance???
From: Ragnar =?ISO-8859-1?Q?Hafsta=F0?= <gnari@simnet.is>
To: pgsql-performance@postgresql.org
Cc: Andrei Bintintan <klodoma@ar-sd.net>, pgsql-sql@postgresql.org
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Date: Thu, 20 Jan 2005 19:23:12 +0000
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On Thu, 2005-01-20 at 19:12 +0000, Ragnar Hafstað wrote:
> On Thu, 2005-01-20 at 11:59 -0500, Greg Stark wrote:
> 
> > The best way to do pages for is not to use offset or cursors but to use an
> > index. This only works if you can enumerate all the sort orders the
> > application might be using and can have an index on each of them.
> > 
> > To do this the query would look something like:
> > 
> > SELECT * FROM tab WHERE col > ? ORDER BY col LIMIT 50
> > 
> > Then you take note of the last value used on a given page and if the user
> > selects "next" you pass that as the starting point for the next page.
> 
> this will only work unchanged if the index is unique. imagine , for
> example if you have more than 50 rows with the same value of col.
> 
> one way to fix this is to use ORDER BY col,oid

and a slightly more complex WHERE clause as well, of course

gnari