public function free()
    {

        switch ($this->mode) {

            case "mysql":
                $this->result->free();
                break;

            case "postgres":
            case "redshift":
                pg_free_result($this->result);
                break;

            case "odbc":
                odbc_free_result($this->result);
                break;

            case "sqlite":
                $this->result->finalize();
                break;

            case "mssql":
                mssql_free_result($this->result);
                break;

            case "mssqlsrv":
                sqlsrv_free_stmt($this->result);
                break;
        }
    }