php PDO如何连接mysql数据库

//第一种写法
	try{
	$dsn = "mysql:host=localhost;dbname=test";
	$db = new PDO($dsn,"root","");
	var_dump($db);
	$sql = "select * from ld_member";
	$statement = $db->query($sql);
	while($result = $statement->fetch(PDO::FETCH_ASSOC )){
           print_r($result);
	}
	$db = null;
		}catch (PDOException $e){
	echo "发生错误。";
	} 
	 
//第二种写法

	$dsn = "mysql:host=localhost;dbname=test";
	$db = new PDO($dsn,"root","");
	$sql = "select * from ld_member";
	$statement = $db->query($sql);
	while($result = $statement->fetch(PDO::FETCH_ASSOC )){
           print_r($result);
	}