Datatables not working in codeigniter

Question

I am new to codeigniter, and using codeigniter 2.1.4. Here i have written query using datatables, but getting no results. In database respected values are there. I don't know what i did wrong, Kindly guide me. This is my code,

controller :

$this->load->library('datatables');
        $this->datatables->select("sales.reference_no,sales.customer_name,sale_items.serial_no,sales.total,
        sales.inv_discount,sales.total_tax2,sales.inv_total,users.username")->from('sales');
        $this->datatables->join('sale_items', 'sales.id = sale_items.sale_id', 'left');
        $this->datatables->join('users', 'sale_items.serial_no = users.id', 'left');

        if($start_date) {
                $this->datatables->where('sale_items.serial_no', $salesman, 'sales.date >=' $start_date, 'sales.date <=' $end_date);
        }else{ 
            $this->datatables->where('sale_items.serial_no', $salesman); 
        }   

   echo $this->datatables->generate();

Answer 1

Finally i got the answer for my question after taking more time. This is the correct one,

$this->load->library('datatables');
        $this->datatables->select("sales.reference_no,sales.customer_name,sale_items.serial_no,sales.total,
                            sales.inv_discount,sales.total_tax2,sales.inv_total,users.username")->from('sales');
        $this->datatables->join('sale_items', 'sales.id = sale_items.sale_id', 'left');
        $this->datatables->join('users', 'sale_items.serial_no = users.id', 'left');

        if($start_date) {
                $this->datatables->where('sale_items.serial_no', $salesman, 'sales.date >=', $start_date, 'sales.date <=' , $end_date);
        }else{ 
            $this->datatables->where('sale_items.serial_no', $salesman); 
        }   

   echo $this->datatables->generate();