public function isReadOnly()
    {
        $readOnly = false;
        $fields   = $this->getPart(Zend_Db_Table_Select::COLUMNS);
        $cols     = $this->_info[Zend_Db_Table_Abstract::COLS];

        if (!count($fields)) {
            return $readOnly;
        }

        foreach ($fields as $columnEntry) {
            $column = $columnEntry[1];
            $alias = $columnEntry[2];

            if ($alias !== null) {
                $column = $alias;
            }

            switch (true) {
                case ($column == self::SQL_WILDCARD):
                    break;

                case ($column instanceof Zend_Db_Expr):
                case (!in_array($column, $cols)):
                    $readOnly = true;
                    break 2;
            }
        }

        return $readOnly;
    }