getCustomer($customer_id)
and getCustomers($data = array())
are the functions used to get customer data.
Since they are SELECT *
querys your field is being processed automatically.
Afterwards you need to go in the Controller section in the controller\sale folder and there you have customer.php, custom_field.php and and edit the ones that you need. For example:
$this->data['customers'][] = array(
'customer_id' => $result['customer_id'],
'name' => $result['name'],
'email' => $result['email'],
'customer_group' => $result['customer_group'],
'status' => ($result['status'] ? $this->language->get('text_enabled') : $this->language->get('text_disabled')),
'approved' => ($result['approved'] ? $this->language->get('text_yes') : $this->language->get('text_no')),
'ip' => $result['ip'],
'date_added' => date($this->language->get('date_format_short'), strtotime($result['date_added'])),
'selected' => isset($this->request->post['selected']) && in_array($result['customer_id'], $this->request->post['selected']),
'action' => $action
);
add your field in this array (this is from customer.php).
And finally edit the .tpl files that are called from the view\template\sale folder so they appear where they want them to.
Hope i was clear enough.