一句代碼：

SELECT FLOOR(10000 + RAND() * 89999) AS random_number

FROM table1

WHERE "random_number" NOT IN (SELECT unique_id FROM table2)

LIMIT 1

隨機生成5位數字，并且不重復。上面的代碼真是給人無限的聯想力。

例如：

function get_unique_username($chance=10,$show_sql=FALSE)

{

global $conn;

// connect db

if(!$conn) connect();

$output = FALSE;

$rand = rand(1,$chance);

$sql = 'SELECT FLOOR('.($rand==5?'10000 + RAND() * 89999':'100000 + RAND() * 899999').') AS random_number FROM gm_users WHERE "random_number" NOT IN (SELECT unique_id FROM gm_ids) LIMIT 1';

if($show_sql) echo $sql;

$result = mysql_query($sql);

$row = mysql_fetch_assoc($result);

if($row['random_number'])

{

$output = $row['random_number'];

// insert this random_number to table gm_ids

insert('gm_ids', array('unique_id'=>$output));

}

return $output;

}

以上實例為，隨機生成5或6位數字，并且生成5位數字的記錄是 1/10 ($chance)