I am building a site and using mysqli to access my database. I am just about to embark into a tutorial from phpAcademy written in PDO. my question is: I know I can use PDO and mysqli on the same page but how about db connection? do I need to create two different connections? can I pass variables from mysqli to pdo and pdo to mysqli? what kind of problem will I encounter along the way by mixing two different styles of communicating with my database?