How to do jquery/ajax partial post after on change event of dropdown

How to to ajax/jquery post on on change event of drop box in php :
I m Using Codeignitor /Grocery Crud framework .

I want to render the same form  having depended dropbox

dropbox1-->  value -->dropbox2 (where clause)

Select value from dropbox1 and create dropbox2 based on parent dropbox1
Puneet AroraFounderAsked:
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I covered this dropdown list dependency here:

It should help you do the front-end (binding a function to the first dropdown, emitting an POST ajax request upon change, grabbing the result and then populate the second/dependent dropdown).  Notice that on the backend the poster is sending a json-encoded string with a key/property named "options" which contains the <option> tags for the second <select>.
Puneet AroraFounderAuthor Commented:
Dear hielo ,

I have checked the comments for right solution  , And found that I m doing similar to
what you are suggesting ...!  But I found difference in the ajax syntax , so here it is :

<script src="//"></script>
      alert('Entered the Ready Function');
                  alert('Entered Chnage Function');
            var country_id = $('#country').val();
            if(country_id != 0)
                        success: function(returndata){

I also found that it is giving me status OK 200 using FireBug, and finds the controller "getValue.php" , But I
want the selected value /id to be printed/echo also on  getValue.php and then
the child dropdown renders on from where the post was made .. The getValue is
not echo or printing any value ..? I don't know  why ? I m using Codeignitor /Grocery  Frameworks
Look at my second post on the link above.  That is basically what you need in getValue.php -- query the db; dynamically create the html <option> tags while iterating over the records; echo the result of jason_encode.  Basically all you need to change are the db connection credentials (on that post it is understood that these are in db.php) and the select query.

>> I also found that it is giving me status OK 200 using FireBug
Are you referring to the ajax call or the loading page?

>>But I want the selected value /id to be printed/echo also on  getValue.php
But if you are emitting an ajax call, the "current" page never changes.  So the country_id you are sending to the server (via ajax) should still be on the browser window -- you shouldn't have to echo it back.

It would help if you post a link to a "test page".

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Puneet AroraFounderAuthor Commented:
Now , it is working : ajax call
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