Providing an ad-hoc report facility for business using in MySQL and PHP?
I suppose you could wire up some gnarly PHP code that queries INFORMATION_SCHEMA for database objects and then presents them to your end-users using some glamorous jquery and HTML5 elements. Then you'd have to generate SQL from the user's input. 

Or, you could go through a bit of effort to implement/deploy BIRT to your user base.

However, my personal preference for doing ad-hoc querying would probably be Pentaho. There's still the overhead of deploying this to your users, but I find their documentation and implementation to be straightforward and easy-to-follow. Here's a link to using Ad-Hoc reporting in the Pentaho suite.