Message-ID: <500F818F.1020106@edgesoft.cn>
Date: Wed, 25 Jul 2012 13:18:07 +0800
From: wangqi <wangqi@edgesoft.cn>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: pgsql-admin@postgresql.org
Subject: Re: about select use random
References: <500F5870.8010400@edgesoft.cn> <12603.1343184929@sss.pgh.pa.us>
In-Reply-To: <12603.1343184929@sss.pgh.pa.us>
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Hi Tom

If you don't want that, you can use a WITH to lock down the result of a
single random() call.


How should I do it?


=D3=DA 2012-7-25 10:55, Tom Lane =D0=B4=B5=C0:
> wangqi <wangqi@edgesoft.cn> writes:
>> =A1=F6SQL-3
>> select * from wk_mclid1 where id1=3D (round((random() * (10-1))::integ=
er)
>> + 1)::integer;
>> When we excute SQL-3,sometimes the result was 0 record or more than 1
>> record.
>> Why?
> random() is re-evaluated for each row scanned by the SELECT.
>
> If you don't want that, you can use a WITH to lock down the result of a
> single random() call.
>
> 			regards, tom lane
>


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