Question

我需要通过添加或减去数值来更新当前的DB字段值。我已经审核了＃34;建议的答案＆＃34;并没有找到解决我的问题的方法。我的数据库中的字段是标题＆＃34;信用＆＃34;它的默认值为＆＃34; 0。＆＃34;指定的数据库引擎是InnoDB。我使用程序化PHP编码，以下是我目前的代码：

定义变量

    $id=$_SESSION['user_id'];  //id number for user
    $amount=$_POST['Amount']; //value of charges 12 character string
    $amount=ltrim($amount, '0'); //eliminates leading 0's
    $credit=$amount/1000; //converts value to credits
    $credit=number_format($credit, 2);  //formats credits with two decimal points

然后我建立数据库连接并执行以下查询

    $q="select credits from registration WHERE user_id=$id";
    $r=mysqli_query ($dbc, $q);
    $update="UPDATE registration SET credits = credits + $credit WHERE user_id=$id";

如果我＆＃34;回声＆＃34;变量我看到所有的值，但＆＃34;更新＆＃34;失败。使用程序性的PHP编码，需要修改什么来逐步更新＆＃34;信用＆＃34;场？

Answer 1

//**i hope this helps**

<?php
$id=$_SESSION['user_id'];  //id number for user
$amount=$_POST['Amount']; //value of charges 12 character string
$amount=ltrim($amount, '0'); //eliminates leading 0's
$credit=$amount/1000; //converts value to credits
$credit=number_format($credit, 2);  //formats credits with two decimal points

$credits; // the credits from query select will be stored here

/* edit with your database parameters */
       $mysqli = new mysqli($host, $user, $password, $db);

       if(mysqli_connect_errno()) {
          echo "Connection Failed: " . mysqli_connect_errno();
          exit();
       }

       mysqli_set_charset($mysqli,"utf8");

if($stmt = $mysqli -> prepare("select credits from registration WHERE user_id=?"))
{
 $stmt -> bind_param("i", $id); //'i' means that ? is an integer value, and $id is the parameter for this value
 $stmt -> execute();
 $stmt -> bind_result($credits);
 $stmt -> fetch();
 $stmt -> close();

 $total=$credits+$credit;
 if($stmt = $mysqli->prepare("UPDATE registration SET credits = ? WHERE user_id=?"))
 {
  $stmt->bind_param("di",$total,$id);
  $stmt->execute();
  echo 'oki doki';
  $stmt->close();
 }

}

?>

Answer 2

关闭，我想提供解决我的问题的编码，它可以帮助任何人查看此帖子。我相信Dante的解决方案使用＆＃34;准备好的陈述＆＃34;是最好的，但这是我如何解决我的问题。

代码行添加：

    $update="UPDATE registration SET credits=$ttl WHERE user_id=$id";  
    $r = mysqli_query ($dbc, $update) or trigger_error("Query: $update\n<br />MySQL Error: " . mysqli_error($dbc));

将更新查询修改为：

{{1}}

这很好用，我需要向用户发送消息中的$ ttl和$ credit变量。我希望这会有所帮助。

增量更新数据库字段

2 个答案: