MySQL get a random value between two values - php

Question

I have two columns in a row: min_value, max_value. Is there a way to do a select like:
SELECT RAND(`min_v`, `max_v`) `foo` [..]
I do realize that RAND does a different thing; the closest I came up (with help) is (RAND() * (max-min))+min, though it will produce a float number, which I'd need then to ROUND() and this is just completely wrong.
Unless anyone can suggest an alternative (which would be very useful), I will go PHP way.

Answer 1

Actually, ROUND((RAND() * (max-min))+min) is the best way in MySQL to do what you'd like. It is also the best way in ActionScript, JavaScript, and Python. Honestly, I prefer it to the PHP way because it is more convenient.
Because I don't know how many rows you'll be returning, I can't advise you whether it is better to use PHP or MySQL for this, but if you're dealing with a large number of values you probably are better off using MySQL.
Addendum
So, there was a question as to whether this is better in PHP or MySQL. Instead of getting into a debate on principles, I ran the following:
<pre><?php
$c = mysql_connect('localhost', 'root', '');
if(!$c) die('!');
echo mysql_select_db('test', $c)?'Connection':'Failure';
echo PHP_EOL;
echo ':::::::::::::::::::::::::BEGINNING MYSQL RAND::::::::::::::::::::::::::::::'.PHP_EOL;
$start = microtime(1);
for( $i = 0; $i < 100000; $i++ )
{
$r = mysql_query( 'SELECT ROUND(RAND() * (200-10) + 10) FROM dual' );
$r = mysql_fetch_array( $r );
}
$end = microtime(1);
echo ($end - $start) . " for MySQL select".PHP_EOL;
echo ':::::::::::::::::::::::::BEGINNING PHP RAND::::::::::::::::::::::::::::::' .PHP_EOL;
$start = microtime(1);
for( $i = 0; $i < 100000; $i++ )
{
$r = mysql_query( 'SELECT 200 AS two, 10 AS tem FROM dual' );
$r = mysql_fetch_array( $r );
$r[2]= rand($r[0], $r[1]);
}
$end = microtime(1);
echo ($end - $start) . " for PHP select".PHP_EOL;
MySQL is faster by about 2-3%.
If you use this, however (note, more columns return by MySQL):
<pre><?php
$c = mysql_connect('localhost', 'root', '');
if(!$c) die('!');
echo mysql_select_db('test', $c)?'Connection':'Failure';
echo PHP_EOL;
echo ':::::::::::::::::::::::::BEGINNING MYSQL RAND::::::::::::::::::::::::::::::'.PHP_EOL;
$start = microtime(1);
for( $i = 0; $i < 100000; $i++ )
{
$r = mysql_query( 'SELECT ROUND(RAND() * (200-10) + 10) as rd, 200 as two, 10 as ten FROM dual' );
$r = mysql_fetch_array( $r );
}
$end = microtime(1);
echo ($end - $start) . " for MySQL select".PHP_EOL;
echo ':::::::::::::::::::::::::BEGINNING PHP RAND::::::::::::::::::::::::::::::' .PHP_EOL;
$start = microtime(1);
for( $i = 0; $i < 100000; $i++ )
{
$r = mysql_query( 'SELECT 200 AS two, 10 AS tem FROM dual' );
$r = mysql_fetch_array( $r );
$r[2]= rand($r[0], $r[1]);
}
$end = microtime(1);
echo ($end - $start) . " for PHP select".PHP_EOL;
MySQL comes out behind by 3-4% (very inconsistent results) (about the same results if you don't use an array index assignment for $r[2]).
The major difference, it seems, comes from the number of records return to PHP and not the randomization system itself. So, if you need column A, column B, and a random value, use PHP. If you only need the random value, then use MySQL.

Answer 2

This method guarantees the same statistical probability for each value:
SELECT FLOOR((RAND() * (max-min+1))+min)

Answer 3

in case minimum range is 1, you can simply
SELECT FLOOR((RAND() * max_range) + 1)
in case minimum range is 0, you can even more simply
SELECT FLOOR((RAND() * max_range))

Answer 4

Could you do something like this?
SELECT id, (FLOOR( 1 + RAND( ) *60 )) AS timer
FROM users
LIMIT 0 , 30
See this post

Answer 5

Depending on how many rows you have in the table(s), using rand() in a query or subquery can be extremely slow.
You can seriously improve the speed by first putting the random value in a variable and then just using that in your query.
For example on a table with over 4 million rows...
This took over 10 minutes:
SELECT
*
FROM
`customers` `Customer`
WHERE
`id` = (
SELECT
FLOOR((RAND() * (max(`CustomerRand`.`id`) - min(`CustomerRand`.`id`) + 1)) + min(`CustomerRand`.`id`)) `random_id`
FROM
`customers` `CustomerRand`
);
While this took about 3 seconds on average:
SELECT
FLOOR((RAND() * (max(`CustomerRand`.`id`) - min(`CustomerRand`.`id`) + 1)) + min(`CustomerRand`.`id`)) `random_id`
FROM `customers` `CustomerRand` INTO #rand_id;
SELECT * FROM `customers` WHERE `id` = #rand_id;
You might even be able to put this into a stored procedure then if it's something you would want to do or re-use often. The stored procedure could then be called from PHP or Python or wherever

Answer 6

You can use order by rand
SELECT virtual.num
FROM (
SELECT 1 AS num UNION
SELECT 2 AS num UNION
SELECT 3 AS num
) virtual
ORDER BY RAND()
LIMIT 1