protected function gridDiscountColumn($data, $row)
{
$criteria = new CDbCriteria();
$criteria->select = 'SUM(discount) as discount';
$criteria->condition = 'invoice_id= :invoiceId';
$criteria->params = array(':invoiceId' => $data->id);
$product = InvoiceItem::model()->find($criteria);
if ($product) {
print_r($product->discount);
} else {
print_r(0);
}
}
