Date: Sat, 18 Nov 2006 18:52:16 +0100
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: Random()
Message-ID: <20061118175216.GA1444@a-kretschmer.de>
References: <55c095e90611161031h7a1ce42chd9a59a53ba7e7028@mail.gmail.com>
	<20061116191632.GA21285@a-kretschmer.de>
	<a97c77030611180932q26af1cd3h8fb33a0fe4e3dd89@mail.gmail.com>
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am  Sat, dem 18.11.2006, um 23:02:33 +0530 mailte Rajesh Kumar Mallah folgendes:
> >select <bigint_column> from <your_table> order by random() limit 1;
> 
> This query will tend to get slower as the table grows because of the 
> sorting.

Right.


> 
> it possible to get a row from a random offset
> how about
> 
> select <bigint_column> from <your_table>  limit 1 offset  20000*random() ;

For instance, you have a table with only 500 rows and random() returns
0.999? In other words: in think, this is a bad idea, unless you use a
constant for the offset-calculation thats not larger than the number of
rows in this table. For this, you need this value, but select count(1)
from table force a seqscan -> slow.


Andreas
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Andreas Kretschmer
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