From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: Random()
Date: Sat, 18 Nov 2006 18:52:16 +0100
Message-ID: <20061118175216.GA1444@a-kretschmer.de> (raw)
In-Reply-To: <a97c77030611180932q26af1cd3h8fb33a0fe4e3dd89@mail.gmail.com>
References: <55c095e90611161031h7a1ce42chd9a59a53ba7e7028@mail.gmail.com>
<20061116191632.GA21285@a-kretschmer.de>
<a97c77030611180932q26af1cd3h8fb33a0fe4e3dd89@mail.gmail.com>
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
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47215, D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: andreas.kretschmer@schollglas.com
Subject: Re: Random()
In-Reply-To: <20061118175216.GA1444@a-kretschmer.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox