我有以下疑问：

$this->db->select('SUM(cost_price) AS cost_price,SUM(cost_price) AS total,employees.username AS staff_name');
        $this->db->from('items');
        $this->db->join('customers', 'customers.person_id = items.customer_id');
        $this->db->join('employees', 'employees.person_id = items.staff_id');
        $this->db->join('people', 'people.person_id = customers.person_id');
 $this->db->group_by('items.is_serialized');

在items表中，我有一个名为is\u serialized的字段，我想对is\u serialized字段中具有值的所有行进行分组，但不分组如果该行为null，是否可以使用我的查询进行分组？