1First, add an id to age group
2
3<select name="age_group" id="age_group">
4Then
5
6$( document ).ready(function() {
7 $('#age_group').change(function(){
8 $.ajax({
9 type: "POST",
10 url: "ajax.php",
11 data: { group_id: $(this).val() },
12 dataType: "html"
13 })
14 .done(function( msg ) {
15 $('#hobbies').html(msg);
16 });
17 });
18});
19In ajax.php you get all hobbies where group_id = $_POST['group_id']
20
21$sql = "SELECT name FROM tbl_hobbies WHERE group_id = ".$_POST['group_id'];
22// Execute your query and put the result in a variable (example $result_query)
23// Then loop it
24foreach($result_query as $row) {
25 echo '<option>'.$row['name'].'</option>';
26}
27NB : The loop may change according to your method to retrieve data