I recently read an article from John Wiseman on creating a MySQL connection with AJAX (article link). Being a newcomer to the AJAX world I've found many tutorials and code libraries to be rather bloated and presumptious. John's article however was right on target and really got me going in the write direction to start thinking about AJAX and how it should work.

Given that article I started tinkering around and wound up creating a simple shopping cart application for a client. Below is a scaled down version of said application that hopefully can help you along in your AJAX travels.

There's plenty of code here to get you started, including the database structure, all availible for download. He doesn't explain much of it, but he does show where the Ajax is used - adding/removing/etc products from the shopping cart...