Insert random number in database

I want to add a random number to the records in de database. I use a function to generate a 12 digit number.

When I run the insert it always inserts the same number (not random). When I just echo a random number it works fine.

---

function randomNumber($length) {
$min = 1 . str_repeat(0, $length-1);
$max = str_repeat(9, $length);
return mt_rand($min, $max);   
}


$query = mysql_query("SELECT * FROM `events` WHERE  `id` = '39' ") or die(mysql_error());

        if(mysql_num_rows($query) > 0) {

        $row = mysql_fetch_object($query);

        for ($i=1; $i <= $row->number; $i++) {      

                $ean = randomNumber(12);

                mysql_query("INSERT INTO    `events_tickets` 
                                            (`order_id`,`ticket_id`) 
                                VALUES (
                                            '" . intval($row->id) . "',
                                            '" . $ean. "'
                                        )
                            ");




        }


    }

echo randomNumber(12);