codeigniter multiple form in one page html insert data in database

 codeigniter multiple form in one page html insert data in database

 public function add_about_us_section_a(){
$this->input->post('sub');
$value = $this->input->post();

      $data = array(
      'id' => $value['id'],
'main_heading' => $value['main_heading'],
'sub_heading' => $value['sub_heading'],
'message' => $value['message'],
);
$this->db->where('id',$data['id']);
      $this->db->update('add_about_us',$data);
$this->session->set_flashdata('success_msg', 'Record Add Successfully');
            redirect("admin/add_about_us");
    }

Take submit button name == (sub)