Why didn't you use a php framework like Symphony or Laravel or something even lighter. You've written code that looks so last millenium :D

Never crossed my mind and being that this is my first PHP project I have been learning along the way by example. None of them ever mention a framework. But honestly I always end up hating frameworks (that's why I avoid node.js).

Your SQL queries are written the old way. Why not use PDO with prepared statements for example?

Yes, I need to learn PDO just yet to do so