Magento 1: Add Customer Group in Order Grid

Question

I want to add a column in Sales > Order Grid for "Customer Group" after the "Ship to name" column. I know i need to modify

app/code/core/Mage/Adminhtml/Block/Sales/Order/Grid.php

Could someone please help me with the proper code? Also, i don't want to build a custom module for this column. Thank you!

Using Magento 1.8

Answer 1

Magento 1 customer group id stored in sales_flat_order table while admin order grid fetch collection from sales_flat_order_grid so for getting customer group information must get data from sales_flat_order table.
magento order grid collection & column manage from app/code/core/Mage/Adminhtml\Block/Sales/Order/Grid.php so first join table in _prepareCollection() function as below.

$collection = Mage::getResourceModel($this->_getCollectionClass());
$collection->getSelect()->joinLeft(
    'sales_flat_order',
    'main_table.entity_id = sales_flat_order.entity_id',
    array('customer_group_id')
);
$this->setCollection($collection);

now add customer group column in grid with drop-down option as below (add this in _prepareColumns() function)

$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')->__('Group'),
    'index'         =>  'customer_group_id',
    'filter_index'  =>  'sales_flat_order.customer_group_id',
    'type'          =>  'options',
    'options'       =>  $groups,
));