Обсуждение: Random()

Hi list,<br /><br />I have a bigint collumn and I would like to generate a random number within the numbers of my
column.<br/><br />Is it possible ?<br /><br /><br /><br
/>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-<br
/>                                  Atenciosamente(Sincerely)<br />                        Ezequias Rodrigues da
Rocha<br/> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-<br />A pior das democracias ainda é
melhordo que a melhor das ditaduras <br />The worst of democracies is still better than the better of dictatorships<br
/><ahref="http://ezequiasrocha.blogspot.com/">http://ezequiasrocha.blogspot.com/</a> 

am  Thu, dem 16.11.2006, um 16:31:14 -0200 mailte Ezequias Rodrigues da Rocha folgendes:
> Hi list,
> 
> I have a bigint collumn and I would like to generate a random number within the
> numbers of my column.

select <bigint_column> from <your_table> order by random() limit 1;


Andreas
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Andreas Kretschmer
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Thank you so much andreas.

Regards
http://ezequiasrocha.blogspot.com




--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
                                  Atenciosamente (Sincerely)
                        Ezequias Rodrigues da Rocha
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
A pior das democracias ainda é melhor do que a melhor das ditaduras
The worst of democracies is still better than the better of dictatorships
http://ezequiasrocha.blogspot.com/

Just another question. I can trust on this random number ? The rule to it is quite tested ?

I am thinking in implementing a function that return allways a random number. What do you think of the trust of this function (random()) ?

My bigint field has 20,000 numbers and I'd like to make real random (used like lottery).


Regards
Ezequias




--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
                                  Atenciosamente (Sincerely)
                        Ezequias Rodrigues da Rocha
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
A pior das democracias ainda é melhor do que a melhor das ditaduras
The worst of democracies is still better than the better of dictatorships
http://ezequiasrocha.blogspot.com/

On Thu, Nov 16, 2006 at 06:54:42PM -0200, Ezequias Rodrigues da Rocha wrote:
> My bigint field has 20,000 numbers and I'd like to make real random (used
> like lottery).

If you want _real_ random, you have to use a non-computer source for
your randomness.  The best you get on a computer is pseudo-random. 
Often it's very good pseudo-random -- most of the time, good enough
for most purposes -- but it isn't true randomness of the sort that is
delivered by (for example) particle decay.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The plural of anecdote is not data.    --Roger Brinner

On 11/16/06, A. Kretschmer <andreas.kretschmer@schollglas.com> wrote:
Is this a PostgreSQL thing or is it SQL standard?

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   Aaron Bono
   Aranya Software Technologies, Inc.
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On 11/17/06, A. Kretschmer <andreas.kretschmer@schollglas.com> wrote:
> am  Thu, dem 16.11.2006, um 16:31:14 -0200 mailte Ezequias Rodrigues da
> Rocha folgendes:
> > Hi list,
> >
> > I have a bigint collumn and I would like to generate a random number
> within the
> > numbers of my column.
>

> 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.

it possible to get a row from a random offset
how about

select <bigint_column> from <your_table>  limit 1 offset  20000*random() ;

?

regds
mallah.




>
>
> Andreas
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> Andreas Kretschmer
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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