public function unlockTables()
    {
        switch ($this->mode) {

            case "mysql":
                $query = "UNLOCK TABLES";
                break;

            case "postgres":
            case "redshift":
            case "odbc":
                $query = "COMMIT";
                break;

            default:
                throw new \Exception("unlockTables() not supported in this mode (" . $this->mode . ")");
        }

        return $this->query($query);
    }