title: Magento - How to add country column in Orders grid filter?
body: <p>I tried:</p>
  
  <pre><code>$collection = Mage::getResourceModel($this-&gt;_getCollectionClass());
          $collection-&gt;oinAttribute('billing_country_id', 'customer_address/country_id', 'default_billing', null, 'left');
          $this-&gt;setCollection($collection);
          return Mage_Adminhtml_Block_Widget_Grid::_prepareCollection();
  </code></pre>
  
  <p>but results are blank.
  Please Help me add country column in Orders grid. Thanks.</p>