function alterTable($name, $changes, $check)
    {
        $db =& $this->getDBInstance();
        if (PEAR::isError($db)) {
            return $db;
        }

        foreach ($changes as $change_name => $change) {
            switch ($change_name) {
            case 'add':
            case 'remove':
            case 'change':
            case 'rename':
            case 'name':
                break;
            default:
                return $db->raiseError(MDB2_ERROR_CANNOT_ALTER, null, null,
                    'change type "'.$change_name.'" not yet supported', __FUNCTION__);
            }
        }

..