callback for select form element.

Hi fellas,

I need some help with the following:

In a form I have 2 form elements: a select and one table (custom element).

Now based on the selection in the select form element, I want to populate the table element via DB query.Everytime the selection in the select element changes,I want to refresh the table contents i.e. I need a callback.

For this purpose,what callback should I use?

I have tried out #element_validate,#post_render and #process but they dont seem work for this purpose.

Appreciate any help.