On 25 May 2013 17:56, Ian Lawrence Barwick <barwick@xxxxxxxxx> wrote:
2013/5/26 bricklen <bricklen@xxxxxxxxx>:
somewhat shorter:>
> On Sat, May 25, 2013 at 8:45 AM, Karel Riveron Escobar
> <kescobar@xxxxxxxxxxxxxxxxxx> wrote:
>>
>> I want to generate random numbers in Pl/pgSQL. How can I do this?
>> To be more specific, I have to generate random numbers among 0 and 5.
>
>
> One way:
> select n from unnest(ARRAY[0,1,2,3,4,5]) n order by random() limit 1;
SELECT (random() * 5)::INT
I'd rather use something like:
SELECT floor(random()*6)::INT
as this gives uniform results distribution.
Compare the two below queries, in the first you have twice less results for 0 and 5 than for the rest numbers.
WITH x AS (SELECT (random()*5)::INT r FROM generate_series(1,1000*1000)) SELECT r, count(*) FROM x GROUP BY r ORDER BY r ;
WITH x AS (SELECT floor(random()*6)::INT r FROM generate_series(1,1000*1000)) SELECT r, count(*) FROM x GROUP BY r ORDER BY r ;
regards
Szymon
