While reworking our initial code completion implementation in MySQL Workbench I developed an approach that can potentially be applied for many different situations/languages where you need code completion. The current implementation is made for the needs of MySQL Workbench, but with some small refactorings you can move out the MySQL specific parts and have a clean core implementation that you can easily customize to your needs.
Since this implementation is not only bound to MySQL Workbench I posted the full description on my private blog.