Checking if it exists in mysql

so I have this script to generate me a random number, but I need it do be unique. I tried to do while script to check if it already exists in database but it doesn't work for me.

 $numbers = range(6, 1);
    $random = '';
    shuffle($numbers);
    foreach ($numbers as $number) {
        $random.= $number;
    }

This is the code I tried to work with

    var stop_cycle = 0;

while (!stop_cycle) {
$numbers = range(6, 1);
    $random = '';
    shuffle($numbers);
    foreach ($numbers as $number) {
        $random.= $number;
    }
$db->query("SELECT upload_ID FROM uploads WHERE upload_ID = ".$random);

// check if query returns any result
if(mysql_affected_rows() == 0)  {

// DOING STUFF

// end cycle
 stop_cycle=1;
}

}