$server = SERVER
$port = PORT
$user = USER
$password = PASSWORD
$database = DATABASE

### MYSQL ###

$connection = new PDO("mysql:host=$server;dbname=$database;charset=utf8",$user,$password);

### SQLSRV ###

$connection = new PDO("sqlsrv:Server=$server,$port;Database=$database;charset=utf8", $user, $password);

### ORACLE ###

$connection = new PDO('oci:dbname=$server/$port;charset=AL32UTF8', $user, $password);
// or
$tns = "(DESCRIPTION =
          (ADDRESS = (PROTOCOL = TCP)(HOST = $host)(PORT = $port))
            (CONNECT_DATA =
              (SERVER = DEDICATED)
              (SERVICE_NAME = $database)
          )
        )";
$connection = new PDO('oci:dbname=$tns;charset=AL32UTF8',$user,$password');