php中mysql事务回滚无效怎么办

<?php 
    header("Content-type:text/html;charset=utf-8");
    $pdo = new PDO(&#39;mysql:host=localhost;dbname=data&#39;,&#39;root&#39;,&#39;root&#39;);
    $pdo->exec(&#39;set names utf8&#39;);
    $pdo->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);#修改报错模式
  #开启事务
    $pdo->beginTransaction();
    try{
        #第一次操作
        $sql = &#39;delete from books where bId=40&#39;;
        $smt = $pdo->prepare($sql);
        $smt->execute();
        #第二次操作
        $sql = &#39;delete from1 books where bId=39&#39;;
        $smt = $pdo->prepare($sql);
        $smt->execute();
        #成功提交
        $pdo->commit();
    }catch(PDOException $e){
        echo $e->getMessage().&#39;<br>&#39;.$e->getLine();
        #失败撤回
        $pdo->rollBack();
    }
 ?>