Create PDOExtendedSingleton.php

This trait allows you to use the PDOExtended class as a singleton.

Example :
class db {
    use PDOExtendedSingleton;
}
db::Cnx('mysql:host=localhost;dbname=test', 'root');
db::Cnx()->SqlColumn("SHOW TABLES");

Since it's a trait, it's only compatible with PHP 5.4.
For use with PHP 5.3, copy/paste the code of the trait inside a new class of your own.