php+Mysqli利用事务处理转账问题实例

<?php   header("Content-type:text/html; charset=utf-8");      $mysqli = new mysqli("localhost", "root", "064319", "php");   $mysqli->set_charset("utf8");      if($mysqli->connect_errno) {    die('数据库连接失败'.$mysqli->connect_error);   }      $mysqli->autocommit(false); //自动提交模式设为false   $flag = true; //事务是否成功执行的标志      $query = "update account set balance=balance-1000 where id=3";   $result = $mysqli->query($query);   $affected_count = $mysqli->affected_rows;   if(!result || $affected_count == 0) {  //失败    $flag = false;     }      $query = "update account set balance=balance+1000 where id=2";   $result = $mysqli->query($query);   $affected_count = $mysqli->affected_rows;   if(!$result || $affected_count == 0) {    $flag = false;   }      if($flag) {    $mysqli->commit();    echo '转账成功';   } else {    $mysqli->rollback();    echo '转账失败';   }      $mysqli->autocommit(true); //重新设置事务为自动提交   $mysqli->close(); ?>