Re: advice on weighted random selection

On Sun, 9 Mar 2003 13:40:30 -0800, Jeff Davis
<jdavis-pgsql(at)empires(dot)org> wrote:
>I would like to select (data1,data2) from a random record, but I'd like (1,2)
>to be 3.44 times as likely as (5,6). I would also like (7,8) to be 2 times as
>likely as (5,6), and (1,2) to be 1.72 times as likely as (7,8).

If you had

data1 data2 weight minw maxw
--------------------------------------
1 2 3.44 0.00 3.44
3 4 0.94 3.44 4.38
5 6 1.00 4.38 5.38
7 8 2.00 5.38 7.38

and an immutable wrapper function around random(), you could

SELECT data1, data2
FROM t
WHERE minw < myrandom(7.38) AND myrandom(7.38) <= maxw;

Make sure myrandom() never returns 0.00 or set minw to something less
than 0.00 in the first row.

Servus
Manfred