Преобразовать вложенный SQL-запрос в формат Codeigniter

Question

Мне нужно, чтобы простой запрос MySQL был преобразован в Codeigniter в виде таблиц данных.

Вот фактический запрос.

SELECT distouter.*,
       SUM(purinrout.purchase_ammount) AS prevmonth 
    FROM (SELECT donr.*, 
               SUM(purinr.purchase_ammount) AS curmonth 
        FROM   district_owner AS donr 
               left join district AS dist 
                      ON donr.district_id = dist.id 
               left join franchise AS franinr 
                      ON franinr.district_id = donr.district_id 
               left join purchase AS purinr 
                      ON purinr.f_id = franinr.id 
        WHERE  donr.district_id = '1' 
               AND purinr.purchase_date BETWEEN 
                   Date_format(Curdate(), '%Y-%m-01') AND 
                   Curdate()) AS distouter 
       left join district AS distout 
              ON distouter.district_id = distout.id 
       left join franchise AS franinrouter 
              ON franinrouter.district_id = distouter.district_id 
       left join purchase AS purinrout 
              ON purinrout.f_id = franinrouter.id 
WHERE  distouter.district_id = '1' 
       AND Month(purinrout.purchase_date) = Month(Date_sub(Curdate(), 
                                                  interval 1 month))

Вот что я сделал

$this->CI()->datatables->select('district_owner.*');
    $this->CI()->datatables->select('SUM(purchase.purchase_ammount) AS curmonth');
    $this->CI()->datatables->from('district_owner');
    $this->CI()->datatables->join('district', 'district_owner.district_id = district.id','left');

    $this->CI()->datatables->join('franchise', 'franchise.district_id = district_owner.district_id','left');
    $this->CI()->datatables->join('purchase', 'purchase.f_id = franchise.id','left');
    //$this->CI()->db->where('district_owner.deleted_on', '0000-00-00 00:00:00');
    $this->CI()->datatables->where('district_owner.district_id', '1');
    $this->CI()->datatables->where('purchase.purchase_date BETWEEN 
               Date_format(Curdate(), "%Y-%m-01") AND 
               Curdate()');

    $sub_query = $this->CI()->datatables->generate('json', 'UTF-8');

Я создал sub_query, как вы можете видеть выше, а затем передал его в основном запросе, как показано ниже

$this->CI()->datatables->select('distouter.*');
    $this->CI()->datatables->select('SUM(purinrout.purchase_ammount) AS prevmonth');
    $this->CI()->datatables->from('($sub_query) AS distouter');
    $this->CI()->datatables->join('district', 'distouter.district_id = district.id ','left');

    $this->CI()->datatables->join('franchise', 'franchise.district_id = distouter.district_id','left');
    $this->CI()->datatables->join('purchase', 'purchase.f_id = franchise.id','left');
    //$this->CI()->db->where('district_owner.deleted_on', '0000-00-00 00:00:00');
    $this->CI()->datatables->where('distouter.district_id', '1');
    $this->CI()->datatables->where('Month(purchase.purchase_date)','Month(Date_sub(Curdate(),interval 1 month)');
    return $query = $this->CI()->datatables->generate('json', 'UTF-8');

Но он не работает. Пожалуйста, сообщите мне решение. Данные не являются обязательными. Так что, если вы можете предложить мне ответить, не используя таблицы данных, это тоже сработает.

Спасибо, Махеш