Re: about select use random

Thanks Tom, I try it.


于 2012-7-25 10:55, Tom Lane 写道:
> wangqi <wangqi@edgesoft.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
>


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