This project, called dbrb, implements a client-server database independent interface. Its architecture is based on a server program that interfaces to one or more RDBMS and clients that interact with the server using a simple protocol. The application program (in C, Perl, Php, Java etc.) does not talk directly to the RDBMS but forwards its queries to the dbrb server which in turn forwards them to the database engine. The databases supported are mysql and postgres. If you want to try it click here. There are additional interface modules for informix,db2,oracle and msql here.