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Re: about select use random

From: wangqi <wangqi(at)edgesoft(dot)cn>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: about select use random
Date: 2012-07-25 03:33:02
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-admin
Thanks Tom, I try it.

于 2012-7-25 10:55, Tom Lane 写道:
> wangqi <wangqi(at)edgesoft(dot)cn> writes:
>> ■SQL-3
>> select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
>> + 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

Yours sincerely,
Qi Wang
                         Edgesoft (China) Co.,Ltd
                         F26th Block B,Zhongli Building,
                         No.32 Huoju Road,
                         Hi-Tech Zone,Dalian,China

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