[Xenon]

that means you have to write a script which selects u the rows to update at first:

PHP Code:

<?php
require('./global.php');
$users=$DB_site->query("SELECT user.userid FROM user LEFT JOIN userfield USING (userid) WHERE user.usergroupid=5 AND userfield.field8='United Kingdom'");
$userids = '(0';
while($user=$DB_site->fetch_array($users)) {
$userids .= ','.$user['userid'];
}
$userids .= ')';
$DB_site->query('UPDATE user SET usergroupid=8 WHERE userid IN '.$userids);

?>