activerecord - Get the result of SUM and group field from Active record in Codeigniter -

i need build query in codeigniter don't know how result of sum:

select      description, sum(amount)     payment     (date_payment between '2014-02-01 00:00:00' , '2014-02-28 23:59:59') group description; 

i'm trying result this:

$qwer = $this->db->query("     select description, sum(amount)     payment     (date_payment between '$min_date' , '$max_date')     group description;");  $i = 0; foreach ($qwer->result() $payment) {     $det_payment[$i] = array(         'description'=>$payment->description,         'amount'=>$payment->amount     );     $i++; } 

of course "$payment->amount" wrong, if use alias sum, model doesn't work.

edit: right can choose between description or sum, can't use both select , select_sum

$this->db->select('description'); //$this->db->select_sum('amount', 'amount'); $this->db->where('date_payment >=', $min_fecha); $this->db->where('date_payment <=', $max_fecha); $this->db->group_by("description"); $qwer = $this->db->get('payment'); 

setting false second parameter, 'select' allows write custom sentence.

$this->db->select('description, sum(amount) amount', false); $this->db->where('date_payment >=', $min_date); $this->db->where('date_payment <=', $max_date); $this->db->group_by("description"); $qwer = $this->db->get('payment'); 

documentation ci2
documentation ci3