PHP+Mysql基于事务处理实现转账功能的方法

<?php
header("Content-Type:text/html;charset=utf-8");
$mysqli=new mysqli("localhost","root","","test");
if(mysqli_connect_errno())
{
printf("连接失败:%s<br>",mysqli_connect_error());
exit();
}
$success=TRUE;
$price=8000;
$result=$mysqli->query("select cash from account where name='userA'");
while($row=$result->fetch_assoc())
{
$value=$row["cash"];
echo $value;
}
$mysqli->autocommit(0);
if($value>=$price){
$result=$mysqli->query("UPDATE account set cash=cash-$price where name='userA'");
}else {
echo '余额不足';
exit();
}
if(!$result or $mysqli->affected_rows!=1)
{
$success=FALSE;
}
$result=$mysqli->query("UPDATE account set cash=cash+$price where name='userB'");
if(!result or $mysqli->affected_rows!=1){
$success=FALSE;
}
if($success)
{
$mysqli->commit();
echo '转账成功!';
}else
{
$mysqli->rollback();
echo "转账失败!";
}
$mysqli->autocommit(1);
$query="select cash from account where name=?";
$stmt=$mysqli->prepare($query);
$stmt->bind_param('s',$name);
$name='userA';
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($cash);
while($stmt->fetch())
echo "用户userA的值为：".$cash;
$mysqli->close();
?>
数据库SQL语句如下：
create table account{
userID smallint unsigned not null auto_increment,
name varchar(45) not null,
cash decimal(9,2) not null,
primary key(userID)
)type=InnoDB;
insert into account(name,cash) values ('userA','2000');
insert into account(name,cash) values ('userB','10000');