javascript - 我想从字段 (B) 硬币值中减去字段 (A) - coin_charge 值，并将结果存储在字段 (B) 硬币中

Question

首先，我在 MySQL 数据库中有两个字段，COIN 和 COIN_CHARGE 字段，这是屏幕截图 POPUP Screnshot ,我希望系统检查用户是否单击"is"，即尝试登顶并继续，让系统检查他的数据库 Database screen shot并启动此参数，(如果字段 -coin- 小于字段 -coin_charge-)应该弹出一个窗口，显示资金不足，无法继续充值您的帐户，否则，如果 coin 字段大于 coin_charge 字段，让系统减去coin_charge 来自 coin，即如果 (coin = 100) 且 (coin_charge =50) coin 将变为 50

----------------- 弹出消息 -------------------------- ---

<!-- Trigger the modal with a button -->
<button type="button" class="btn btn-info btn-lg" data-toggle="modal" data-target="#myModal">Report Assignment</button>

<!-- Modal -->
<div id="myModal" class="modal fade" role="dialog">
  <div class="modal-dialog">

    <!-- Modal content-->
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal">&times;</button>
        <h4 class="modal-title">Report Assignment Now!</h4>
      </div>
      <div class="modal-body">
        <p>You Will Be Charge From Your Portal Account, Do You Wish To Continuo?</p>
      </div>
      <div class="modal-footer">
      <a class="btn btn-primary" data-toggle="modal" onClick="$('#createFormId').modal('show')" >YES</a>

        <button type="button" class="btn btn-default" data-dismiss="modal">NO</button>
      </div>
    </div>

  </div>
</div>

----------------------------------------计算代码-------------------- ---------

<?php
    $message_query = mysql_query("select * from student ")or die(mysql_error());
?>

<?php
    while ($row = mysql_fetch_assoc($results)) {
        echo $row['coin'] = $row['coin'] - $row['coin_charge'];
    }
?>

Answer 1

$mysqli = new mysqli("localhost", "username", "password", "dbname");
$userid = $_POST["userid"];

$stmt = $mysqli->prepare('SELECT * FROM student WHERE id = ?');
$stmt->bind_param('i', $userid);
$stmt->execute();

$result = $stmt->get_result();
$row = $result->fetch_assoc();
$stmt->close();

$total = $row['coin'] - $row['coin_charge'];
if($total > 0){
    $stmt = $mysqli->prepare("update student set coin = ? where id = ?");
    $stmt->bind_param("ii", $total, $userid);
    $stmt->execute();
    $stmt->close();
    echo $total;
}else{
    echo 'Insufficient Fund to proceed Top Up your account';exit;
}