Fetch record order by date, even date column as varchar or text.

function get_followupleads($executive_id) {
    $query = "SELECT le.lead_id,le.bname,le.bcontact,le.sname,le.scontact,le.veh_reg_no,le.case_category,le.follow_up_date_time,rto.city as rto_location
              FROM  `rto_tb_leads` as le
              LEFT JOIN rto_office as rto ON rto.id = le.rto_location
              WHERE follow_up_date_time IS NOT NULL AND lead_cre_user_id = $executive_id
              ORDER BY STR_TO_DATE( follow_up_date_time,  '%d-%m-%Y' )";
              $result = $this->db->query($query);
    $details = $result->result_array();
    //echo $this->db->last_query();     
    if( is_array($details) && count($details) > 0 ) {
            return $details;
         }
         return false;
    }