PHP SQL Random Values for each rows

How can I put random values for each row in my database with sql / php. So far I have done this:

$table = "Gauck";
$columnsCw = array("items");
$whereCw   = array('items > :idCw');
$valuesCw  = array('idCw' => 0);

$result_set_cw = $db->select($table, "*", $whereCw, $valuesCw, 15);

foreach($result_set_cw as $result_cw) {
    // var_dump($result_cw);
}

The problem is here that it gives the same random values to every row in my database. But I want that each row get a different value. Can anyone help.