MySQL事务

<?php
//连接数据库
$pdo = new PDO('mysql:host=localhost;dbname=system', "root", '');
//开启事务
$pdo->beginTransaction();

//购买数量
$buynum = $_GET['buynum'];

//产品id
$productid = $_GET['productid'];

//根据购买数量 ,更新库存SQL
$re1 = $pdo->exec("update product set libnum = libnum-{$buynum} where id=" . $productid);

//根据商品的id，获取商品的信息SQL
$sql = "select * from product where id=" . $productid;

//执行获取商品信息SQL语句
$pdoS = $pdo->query($sql);

//得出一维数组结果
$arr = $pdoS->fetch(PDO::FETCH_ASSOC);

//从信息中获取商品单价
$price = $arr['price'];

//用户id
$userid = $_GET['userid'];

//应付金额 (单价*购买数量)
$money = $price * $buynum;

//更新用户表里的余额语句
$sql = "update user set money=money-{$money} where id = {$userid}";

//执行扣钱语句
$re = $pdo->exec($sql);

//如果 库存和余额条件成立
if ($re && $re1) {
    //开启事务
    $pdo->commit();
    echo "购买成功";
} else {
    //回滚
    $pdo->rollback();
    echo "购买失败";
}