How to set a PHP variable using AJAX?

I'm currently working on a project involving a form generator. The user can switch on different databases and add some information from these databases in the form he is building.

I'm working using AJAX, at anytime the user can choose the database开发者_如何转开发 using a select, and on change, it refreshes the list of the database's tables.

What I want to do is, when the database is changed, set a PHP (global maybe ?) variable in order not to have to pass the database as a parameter in each AJAX request I need to do...

(I'm also using jQuery)

Thank you

You could use a SESSION variable for that...