Adding data from customer_entity_varchar to order grid magento - magento

Question

I am trying to add 'accountno' field to order grid from customer_entity_varchar table. To achieve this I changed _prepareCollection() method in Grid.php like this:
protected function _prepareCollection()
{
$collection = Mage::getResourceModel($this->_getCollectionClass());
$customerEntityVarchar = Mage::getSingleton('core/resource')->getTableName('customer_entity_varchar');
$collection->getSelect()->join(array(
'customer_entity_varchar_table'=>$customerEntityVarchar),
'`main_table`.`customer_id`=`customer_entity_varchar_table`.`entity_id`
AND `customer_entity_varchar_table`.`attribute_id`=122',
array('accountno' => 'value'));
print_r($collection->getSelect()->__toString());
$this->setCollection($collection);
return parent::_prepareCollection();
}
In attribute_id=122' 122 is the attribute_id ofaccountno`
When I print_r the select query and execute it in phpmyadmin, it gets me the accurate results back but when I try to add Column to grid in _prepareColumns() method, it shows the field blank.
My _prepareColumns method looks like this:
protected function _prepareColumns()
{
$this->addColumn('real_order_id', array(
'header'=> Mage::helper('sales')->__('Order #'),
'width' => '80px',
'type' => 'text',
'index' => 'increment_id',
));
$this->addColumnAfter('accountno', array(
'header' => Mage::helper('sales')->__('Account No'),
'index' => 'accountno',
), 'real_order_id');
//rest of the code here
}