使用pdo，使用pdo无法插入数据怎么办

<?php
$dbtype = ‘mysql‘;
$dbname = ‘olddream‘;
$user = "root";
$pwd = "wenwajiao";
$ip=‘127.0.0.1‘;
$fuckingcharset = ‘utf8‘;
$dsn = "$dbtype:host=$ip;dbname=$dbname;charset=$fuckingcharset";
$pdo = new PDO($dsn,$user,$pwd);
$rows = $pdo->prepare("select userid,username from userlist");
$rows->execute();
$pdo->beginTransaction();
$ret = $rows->fetchAll();
//update rbac_user set mypass = ? where userid = ?
for($i=0;$i<count($ret);$i++)
{
    $sql = "insert into rbac_user (userid,username,mypass) values (?,?,?)";
    $statement=$pdo->prepare($sql);
    $statement->bindValue(1,$ret[$i][‘userid‘]);
    $statement->bindValue(2,$ret[$i][‘username‘]);
    $statement->bindValue(3,md5($ret[$i][‘userid‘]));
    $statement->execute();
}
$pdo->commit();
$pdo=null;