How to select listbox with options in Ajax PHP jQuery

Question

I have 2 tables in my database call groups and players i am trying to select the group first and then the players show up in another listbox.

DB:

Groups

+-----+---------------+
| id  |  Name         |
+-----+---------------+
| 1   |  Red Group    |
| 2   |  Blue Group   |
| 3   |  Yellow Group |
+-----+---------------+

Players

+-----+-----------+------------+
| id  |  name     |  group_id  |
+-----+-----------+------------+
| 1   |  User1    |  1         |
| 2   |  User2    |  3         |
| 3   |  User3    |  2         |
| 4   |  User4    |  3         |
| 5   |  User5    |  1         |
+-----+-----------+------------+

Answer 1

output group's records at server end, into a select, then ,as vasim said, use jquery's change (http://api.jquery.com/change/) to fire an ajax call which will populate palyers select by the group id.

$('#group').change(function()
{
   $.ajax(
   {
      url: 'url_to_server_script',
      data: 'group='+$('#group').val(),
      success: function(){/* populate here your players select*/}
   });
});

more info about jquery's ajax at http://api.jquery.com/jQuery.ajax/ . depending on what your server script willr eturn you'll have to specify the ajax property datatype (json,xml,...)