public function table_infos($tablename = null)
    {
        if (!empty($tablename)) {
            if (isset($this->tables[$tablename]) && is_array($this->tables[$tablename]))
                return $this->tables[$tablename];
            $query = "PRAGMA table_info ('{$tablename}')";
            $results = $this->arrayQuery($query);
            $this->tables[$tablename] = $results;
            return $results;
        }
        return false;
    }