$rows  = $connection->fetchAll($sql);//this row will return an array

        $collection = new Varien_Data_Collection();

        foreach($rows as $row){
            $rowObj = new Varien_Object();
            $rowObj->setData($row);
            $collection->addItem($rowObj);
        }



        $this->setCollection($collection);
        parent::_prepareCollection();
        return $this;