Surprisingly Magento admin area does not have a “customer group” column under the “Sales > Orders” grid, or under the “Sales > Orders > Create New Order” grid (which is a grid of customers). Why would we need this in a first place? Well, maybe you want to be able to list/filter all the orders in a grid which are purchased by customers from lets say “Dealers” group.
Maybe you want to be able to filter the “Sales > Orders > Create New Order” grid by customer group prior to the actual order creation just to see the total of “Dealers” group customers?

By default “Sales > Orders” grid uses the “sales_flat_order_grid” table for rendering. This table is basically a redundant subset of “sales_flat_order” table. Surprisingly “sales_flat_order” table has the “customer_group_id” column in it, while “sales_flat_order_grid” table does not. So our first step is to add the “customer_group_id” column to the “sales_flat_order_grid” table.

We do so by simple upgrade script that executes the code similar to this:

$installer->getConnection()
        ->addColumn($installer->getTable('sales/order_grid'), 'customer_group_id', array(
            'TYPE' => Varien_Db_Ddl_Table::TYPE_SMALLINT,
            'NULLABLE'  => false,
            'DEFAULT'   => '0',
            'COMMENT' => 'Customer Group'
        ));

If this install/upgrade script executed successfuly we should see the new “customer_group_id” column in the “sales_flat_order_grid” table. Please note that Magento will automatically populate this column from the data in the “sales_flat_order_grid.customer_group_id” once the new orders get saved.

After that we will rewrite the Mage_Adminhtml_Block_Sales_Order_Grid and Mage_Adminhtml_Block_Sales_Order_Create_Customer_Grid but change ony the minimum neceserrr for our new “Customer Group” column to appear.

We do so by adding the proper entries under the config.xml

<global>
<blocks>
    <adminhtml>
        <rewrite>
            <sales_order_create_customer_grid>Mycompany_Myextension_Block_Adminhtml_Sales_Order_Create_Customer_Grid</sales_order_create_customer_grid>
            <sales_order_grid>Mycompany_Myextension_Block_Adminhtml_Sales_Order_Grid</sales_order_grid>
        </rewrite>
    </adminhtml>
</blocks>
</global>

Finally we add the rewrite blocks.

<?php
class Mycompany_Myextension_Block_Adminhtml_Sales_Order_Grid extends Mage_Adminhtml_Block_Sales_Order_Grid
{
    protected function _prepareColumns()
    {
        $groups = Mage::getResourceModel('customer/group_collection')
            ->addFieldToFilter('customer_group_id', array('gt'=> 0))
            ->load()
            ->toOptionHash();
        $this->addColumn('customer_group_id', array(
            'header'    =>  Mage::helper('customer')->__('Customer Group'),
            'width'     =>  '100',
            'index'     =>  'customer_group_id',
            'type'      =>  'options',
            'options'   =>  $groups,
        ));
        $this->addColumnsOrder('customer_group_id', 'shipping_name');
        return parent::_prepareColumns();
    }
}

<?php
class Mycompany_Myextension_Block_Adminhtml_Sales_Order_Create_Customer_Grid extends Mage_Adminhtml_Block_Sales_Order_Create_Customer_Grid
{
    protected function _prepareColumns()
    {
        $groups = Mage::getResourceModel('customer/group_collection')
            ->addFieldToFilter('customer_group_id', array('gt'=> 0))
            ->load()
            ->toOptionHash();
        $this->addColumn('group', array(
            'header'    =>  Mage::helper('customer')->__('Group'),
            'width'     =>  '100',
            'index'     =>  'group_id',
            'type'      =>  'options',
            'options'   =>  $groups,
        ));
        $this->addColumnsOrder('group', 'email');
        return parent::_prepareColumns();
    }
}

And that’s it. Now you should have the “Customer Group” columns on your “Sales > Orders” and “Sales > Orders > Create New Order” grids.