How would be if I would want to generate values among 3 and 5? Regards, Karel Riverón Student Scientific Council Informatics Science University ----- Original Message -----
| From: "Szymon Guz" <mabew...@gmail.com> | To: "Ian Lawrence Barwick" <barw...@gmail.com> | Cc: "bricklen" <brick...@gmail.com>, "Karel Riveron Escobar" | <kesco...@estudiantes.uci.cu>, pgsql-general@postgresql.org | Sent: Saturday, May 25, 2013 12:10:52 PM | Subject: Re: [GENERAL] Random numbers | 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 http://www.uci.cu
