Re: select random order by random - Mailing list pgsql-general

From Lee Keel
Subject Re: select random order by random
Date
Msg-id 76758090F8686C47A44B6FF52514A1D30904E33A@hermes.uai.int
Whole thread Raw
Responses Re: select random order by random  ("Scott Marlowe" <scott.marlowe@gmail.com>)
List pgsql-general
> -----Original Message-----
> From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-
> owner@postgresql.org] On Behalf Of piotr_sobolewski
> Sent: Thursday, November 01, 2007 9:25 AM
> To: pgsql-general@postgresql.org
> Subject: [GENERAL] select random order by random
>
> Dear sirs,
>
> I was very surprised when I executed such SQL query (under PostgreSQL
> 8.2):
> select random() from generate_series(1, 10) order by random();
>
> I thought I would receive ten random numbers in random order. But I
> received
> ten random numbers sorted numerically:
>       random
> -------------------
>  0.102324520237744
>   0.17704638838768
>  0.533014383167028
>   0.60182224214077
>  0.644065519794822
>  0.750732169486582
>  0.821376844774932
>   0.88221683120355
>  0.889879426918924
>  0.924697323236614
> (10 rows)
>
> I don't understand - why the result is like that? It seems like in each
> row
> both random()s were giving the same result. Why is it like that? What
> caused
> it?
>
> --
> Piotr Sobolewski
> http://www.piotrsobolewski.w.pl
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
>        choose an index scan if your joining column's datatypes do not
>        match
[Lee Keel]

Would this not have to do with the 'order by' you added to the end of the
statement?  If you remove the order by clause, then it works for me...

-LK


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