    public static function isExist($user)
    {
        if (isset($_GET['act']) && $_GET['act'] == 'edit') {
            $id = Typo::int($_GET['id']);
            $where = "AND `id` != '{$id}' ";
        } else {
            $where = '';
        }
        $user = sprintf('%s', Typo::cleanX($user));
        $sql = sprintf("SELECT `userid` FROM `user` WHERE `userid` = '%s' %s ", $user, $where);
        $usr = Db::result($sql);
        $n = Db::$num_rows;
        if ($n > 0) {
            return false;
        } else {
            return true;
        }
    }
The software constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component.