add column values from a selected range in code igniter

time-recods table i have

date
time in 
time out 
break in
break out
total_time 

fields in my table. i have this sql query

public function showattendance(){

    $start      = $this->input->post('DATE_FROM');
    $end        = $this->input->post('DATE_TO');
    $employee   = $this->input->post('ID_NUM');

    $sql = "SELECT * FROM `attendance` WHERE (DATE BETWEEN '".$start."' AND '".$end."') AND (ID_NUM = '".$employee."')";

    $query = $this->db->query($sql);

    retu $query->result();
}

now all i want to do is when i already selected the rows between the dates i chose, i wanted to add the selected data from total_time column.