On 25 May 2013 17:56, Ian Lawrence Barwick <barw...@gmail.com> wrote:
> 2013/5/26 bricklen <brick...@gmail.com>: > > > > On Sat, May 25, 2013 at 8:45 AM, Karel Riveron Escobar > > <kesco...@estudiantes.uci.cu> 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; > > somewhat shorter: > 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
