> > On Sat, May 25, 2013 at 8:45 AM, Karel Riveron Escobar > <kescobar@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 ;
