Custome collection query for magento

Custome collection query for magento

protected function _prepareCollection()
{
$collection = Mage::getResourceModel($this->_getCollectionClass());
//echo $collection->getSelect()->__toString();exit;
$collection->getSelect()->join(array(‘sfo’=>’sales_flat_order’),’sfo.entity_id = main_table.order_id’,
array(‘sfo.base_total_online_refunded’,’sfo.base_total_offline_refunded’)
//array(‘sfo.base_total_online_refunded AS refunded_type’)
);

echo ‘<pre>’; print_r($collection->getData());
$this->setCollection($collection);
return parent::_prepareCollection();
}