问PHP：：lastInsertId()返回0

EN

CREATE TABLE IF NOT EXISTS `LastInsertID` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(150) NOT NULL,
  `email` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=6 ;

<?php

// Connect to database
$user = "foo";
$pswd = "bar";

$db = new PDO( 'mysql:host=localhost;dbname=test', $user, $pswd );
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

// Prepare request
$rq = $db->prepare('INSERT INTO `LastInsertID` VALUES(NULL,:name,:email)');

// Begin and commit request
$db->beginTransaction();
$values = array('name'=>'Foo','email'=>'bar@baz.com');
$rq->execute($values);
$db->commit();

// Echo last ID
echo $db->lastInsertId();

?>