By default MySQL is started on port 3306 and MariaDB on port 3307.
Here is an example using PDO to access a database named wordpress installed on MySQL and MariaDB :
$mysql = new PDO('mysql:host=127.0.0.1;port=3306;dbname=wordpress', 'root', '');
$mysqlStmt = $mysql->query("SELECT * FROM wp_comments");
var_dump($mysqlStmt->fetchAll(PDO::FETCH_ASSOC));
$mariadb = new PDO('mysql:host=127.0.0.1;port=3307;dbname=wordpress', 'root', '');
$mariadbStmt = $mariadb->query("SELECT * FROM wp_comments");
var_dump($mariadbStmt->fetchAll(PDO::FETCH_ASSOC));
