Magento 2 – Get Parent Product ID from Child Product ID for Configurable Products

Naing,add parent id filter

$collection = Mage::getModel('sales/order_item')->getCollection()

                       ->addFieldToSelect(array('order_id','sku','name','qty_ordered','product_id','product_options','row_total'))

                       //->setOrder('main_table.order_id', 'desc');
                       ->setOrder('main_table.created_at', 'desc');

        //  $collection->getSelect()->group('main_table.order_id');

To

$collection = Mage::getModel('sales/order_item')->getCollection()
  ->addFieldToSelect(array('order_id','sku','name','qty_ordered','product_id','product_options','row_total'))
    ->addFieldToFilter('parent_item_id',array(
        'null' => true,
        ))->setOrder('main_table.created_at', 'desc');

I added to the answer for others. Only note is, if you try getFinalPrice(); for simple product it will be same results with getSpecialPrice(); that reason I m checking type.

<span class="onsale">
<span>
<?php
    //echo $_product->getTypeId();
    if($_product->getTypeId()!="simple"){
        $label_price=$_product->getSpecialPrice();
        $final_price=$_product->getFinalPrice();
        $save_percent = 100 - round(($final_price / $label_price)*100);
        echo $save_percent.'% Off';
    }else{

        $label_price=$_product->getPrice();
        $final_price=$_product->getSpecialPrice();
        $save_percent = 100 - round(($final_price / $label_price)*100);
        echo $save_percent.'% Off';

    }
    ?>
</span>
</span>