Re: select where id=random()*something returns two results

Rod,

If the table has 100,000 tupples your query is generating 100,000 new
tupples...
Try:

select * from quotes where id = (
select int8( 1 + random() * (
select id from quotes order by id desc limit 1)));

JLL

Rod Taylor wrote:
>
> > select * from quotes where id=1+round(random()* cast ((select max(id)
> > from quotes) as double precision));
> > id | quote |
> > author
> > -----+-----------------------------------------------------------+------
> > -----------
> > 187 | Vergib Deinen Feinden, aber vergiss niemals ihre Namen. | John
> > F. Kennedy
> > 377 | Die Wirklichkeit ist nicht so oder so, sondern so und so. | Harry
> > Mulisch
> > (2 rows)
> >
> > I'm not really into databases, but this sounds wrong. Most of the time,
> > I actually get 0 results.
>
> Random is calculated per call (in this case per comparison). So, the
> value you compare against for 187 is not the same as 377.
>
> UPDATE table SET column = random(); will show the effect.
>
> If you wrap randon() in a subselect, it will cause it to be evaluated
> once:
>
> SELECT * from quotes where id = 1+round((SELECT random()) * cast(....).
>
> However, a much faster query for your purposes would be:
>
> SELECT * FROM quotes ORDER BY random() LIMIT 1;
>
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