Random numbers

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;

2013/5/26 bricklen <bricklen@gmail.com>:

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

Ian Barwick

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

Thanks bricklen.

I found another way in PostgreSQL 9.1.0 Documentation.

SELECT * INTO random_number FROM random(); -- random function gives me a random value among 0.0 -- and 1.0

SELECT * INTO rounded_number FROM round(random_number * 5); -- this line is completly obviously.

Saludos, Karel Riverón
Consejo Científico Estudiantil
Universidad de las Ciencias Informáticas

----- Original Message -----

| From: "bricklen" <bricklen@gmail.com>
| To: "Karel Riveron Escobar" <kescobar@estudiantes.uci.cu>
| Cc: pgsql-general@postgresql.org
| Sent: Saturday, May 25, 2013 11:50:03 AM
| Subject: Re: [GENERAL] Random numbers

| 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;

http://www.uci.cu

On 25 May 2013 17:56, Ian Lawrence Barwick <barwick@gmail.com> wrote:

2013/5/26 bricklen <bricklen@gmail.com>:

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 ;

regards
Szymon

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@gmail.com>
| To: "Ian Lawrence Barwick" <barwick@gmail.com>
| Cc: "bricklen" <bricklen@gmail.com>, "Karel Riveron Escobar"
| <kescobar@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 < barwick@gmail.com >
| wrote:

| | 2013/5/26 bricklen < bricklen@gmail.com >:
|

| | >
|
| | > 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 ;

| regards
| Szymon
http://www.uci.cu

On 25 May 2013 18:14, Karel Riveron Escobar <kescobar@estudiantes.uci.cu>wrote:

How would be if I would want to generate values among 3 and 5?

Hi Karel,
try something like:

SELECT floor(3 + random()*(5-3+1))::INT

Or generally:

CREATE OR REPLACE FUNCTION
random_range(INTEGER, INTEGER) RETURNS INTEGER
AS $$
SELECT floor(($1 + ($2 - $1 + 1) * random()))::INTEGER;
$$ LANGUAGE SQL;

and then:

SELECT random_range(3,5);

regards

Szymon