If you want to add the anthor table
protected function _prepareCollection()
{
$collection = Mage::getResourceModel($this->_getCollectionClass());
$collection->getSelect()->joinLeft('aw_deliverydate_delivery', 'main_table.entity_id = aw_deliverydate_delivery.order_id',array('*' ) );
$this->setCollection($collection);
return parent::_prepareCollection();
}
And the below code in _prepareColumns()
$this->addColumn('aw_deliverydate_delivery', array(
'header' => Mage::helper('sales')->__('Delivery Date '),
'index' => 'aw_deliverydate_delivery',
'type' => 'datetime',
'width' => '100px',
));