onchange

I have 4 combo boxes on my page, the first one populates straight from the table in the database, I would like the second one to populate depending on the first combo boxes selection and the thid combo box to populate depending on the second combo box selection and the fourth combo box to populate according to the selection made in the third combo box. 

Could someone please point me in the correct direction as I have been searching and found nothing I could use.

Thank you.

I used to do this using javascript though it was static data not from a database.

http://stackoverflow.com/questions/1777994/select-country-first-from-a-dropdown-menu-then-region-and-then-city

The accepted answer there seems to be a good way to start, uses AJAX though.