php - How to refresh dropdown without page refresh? -

i having following difficulties:

i fetching value of dropdown mysql , want information displayed in dropdown list.

see this:

<select id="location" name="location" class='form-control'>     <option value="0">select location</option>         <?php             $query = mysql_query("select cityname city");                 while($row = mysql_fetch_assoc($query))                 {                     echo '<option value="'.$row['cityname'].'">'.$row['cityname']. '</option>';                 }         ?> </select> 

by using code populating values database dropdown list, need refresh page values displayed.

thank you.

use jquery ajax

yourfile.php

<select id="location" onchange="getstate(this.value)" name="location" class='form-control'> <option value="0">select location</option>     <?php         $query = mysql_query("select * city");             while($row = mysql_fetch_assoc($query))             {                 echo '<option value="'.$row['cityid'].'">'.$row['cityname']. '</option>';             }     ?> </select>  <select id="state">  </select> 

jquery script

function getstate(city_id) {     var html = $.ajax({         type: "post",         url: "path/to/ajax/my_ajax.php",         data: "city_id=" +city_id,         async: false     }).responsetext;     if(html){         $("#state").html(html);     } } 

ajax.php

$query = mysql_query("select * state city_id=".$_request['city_id']);             while($row = mysql_fetch_assoc($query))             {                 echo '<option value="'.$row['state_id'].'">'.$row['state_name']. '</option>';             }