how to get values from database in codeigniter based on select box value without refreshing page?

There are a few things I noticed

1. $data is an undefined array & you are settings the result array returned by the model function to it's 'res' key
2. dataString is not a json neither it's a js array that you are sending
3. since you used json_encode, you need to use JSON.parse(data) in the ajax success
4. if you do have the result in $data['res'], then you need to do something like this - data=JSON.parse(data)['res']; now you can get id from data[0]

Hope this will help you :

Replace

$root_id = $this->input->post('menu_root_id');

with

$root_id = $this->input->post('name');

Your controller's get_menu_rights method should be like this :

public function get_menu_rights(){  $root_id = $this->input->post('name');  if(! empty($root_id))  {    $data = $this->login_model->get_menu_check($root_id);    // print_r($data);    echo json_encode($data);    exit;      }}

Your ajax success function should be like this :

success: function(data)        {  var html = '';  $.each(data,function(k,v){    alert(v);    html += "<b>menu_code: </b>"+v.menu_code+"<b> menu_name: </b>"+v.menu_name  });  $('#output').html(html); }

I think the query return empty please try this Code.....

 public function get_menu_check($root_id)        {                $data = $this->db->select('C1.menu_code,C1.menu_name')                                 ->from('create_menu as C1')                                 ->where('C1.menu_root_id',$root_id)                                 ->order_by('C1.menu_code')                                 ->get();               if($data->num_rows() >= 0)                  return $data->result_array();               else                  return false;        }