pdo 插入记录用？做占位符

<?php 
header("Content-type: text/html; charset=utf-8");
//设置中国时区
date_default_timezone_set('PRC');

$dsn="mysql:host=127.0.0.1;port=3306;dbname=test;charset=utf8";
$username="root";
$password="root";

$pdo=new PDO($dsn,$username,$password);

// $sql="INSERT INTO student VALUES(NULL,'李鬼','1',36,default,3000,300,'山东')";
// $lines=$pdo->exec($sql);
// var_dump($pdo);
// $sql="INSERT INTO student(name,salary,bonus,city) VALUES (:name,:salary,:bonus,:city)";
$sql="INSERT INTO student(name,salary,bonus,city) VALUES (?,?,?,?)";
$PDOStatement=$pdo->prepare($sql);
$PDOStatement->bindValue(1,'孙二娘');
$PDOStatement->bindValue(2,6000);
$PDOStatement->bindValue(3,900);
$PDOStatement->bindValue(4,'山东');

$PDOStatement -> execute();

// echo "行数：{$lines}";