MySQL获取两个值之间的随机值

发布于07月01日

我一行有两列:min_valuemax_value.有没有办法进行如下 Select :

SELECT RAND(`min_v`, `max_v`) `foo` [..]

我确实意识到RAND的作用不同；我(在帮助下)找到的最接近的数字是(RAND() * (max-min))+min，尽管它会产生一个浮点数，然后我需要将其四舍五入()，这完全是错误的.

除非我建议任何人都可以 Select PHP.

补遗

所以，有一个问题是，这在PHP还是MySQL中更好.我没有就原则进行辩论，而是做了以下几点:

<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的速度提高了2-3%.

但是，如果您使用它(请注意，MySQL会返回更多列):

<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落后3-4%(结果非常不一致)(如果不对$r[2]使用数组索引分配，结果大致相同).

主要的区别似乎来自返回PHP的记录数量，而不是随机化系统本身.因此，如果需要A列、B列和一个随机值，请使用PHP.如果只需要随机值，那么使用MySQL.