public function columnsDoc()
    {
        $ret = str_pad('Name', 25, ' ') . '|' . str_pad('Type', 15, ' ') . '|Info' . "\n";
        $ret .= str_repeat('-', 25) . '|' . str_repeat('-', 15) . '|' . str_repeat('-', 10) . "\n";
        foreach ($this->columns as $name => $info) {
            $ret .= str_pad($name, 25, ' ') . '|';
            $ret .= str_pad($info['type'], 15, ' ') . '|';
            if (isset($info['primary_key'])) {
                $ret .= 'PK ';
            }
            if (isset($info['index'])) {
                $ret .= 'Indexed ';
            }
            if (isset($info['increment'])) {
                $ret .= 'Increment ';
            }
            if (isset($info['default'])) {
                $ret .= 'Default=' . $info['default'];
            }
            $ret .= "\n";
        }

        return $ret;
    }