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();
?>

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');