Re: Random numbers

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" <mabewlun(at)gmail(dot)com>
| To: "Ian Lawrence Barwick" <barwick(at)gmail(dot)com>
| Cc: "bricklen" <bricklen(at)gmail(dot)com>, "Karel Riveron Escobar"
| <kescobar(at)estudiantes(dot)uci(dot)cu>, pgsql-general(at)postgresql(dot)org
| Sent: Saturday, May 25, 2013 12:10:52 PM
| Subject: Re: [GENERAL] Random numbers

| On 25 May 2013 17:56, Ian Lawrence Barwick < barwick(at)gmail(dot)com >
| wrote:

| | 2013/5/26 bricklen < bricklen(at)gmail(dot)com >:
|

| | >
|
| | > On Sat, May 25, 2013 at 8:45 AM, Karel Riveron Escobar
|
| | > < kescobar(at)estudiantes(dot)uci(dot)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