I want collection of orders which belongs from customer_group_id = 4 or customer_group_id = 5. I have applied following filter on collection.
->addFieldToFilter('customer_group_id',Mage::getSingleton('customer/session')->getCustomer()->getGroupId())
This will filter the current user's customer_group_id with database's customer_group_id.
But what i want is, I want to filter on customers those who has customer_group_id equal to either '4' or '5'.
My question is, How should i apply this addAttributeToFilter to achieve that collection.