在 WHERE 子句中使用变量时 PHP MySQL 更新不起作用

Question

我已经检查了这里和其他网站上的数十个线程，但我无法弄清楚为什么我的代码不起作用。我正在尝试使用 PHP 来更新 MySQL，使用变量来标识 WHERE。如果我将变量交换为数字，那么我的代码就可以工作，并且该变量可以在我的脚本中的其他任何地方工作。只是这一行没有。

有问题的行是:

$change = "UPDATE reg_info SET fname='$fname', lname='$lname', email='$email', explevel='$experience', addinfo='$additional', event='$regEvent' where id='$id'";

我还尝试了以下方法:

$change = mysqli_query("UPDATE reg_info SET fname='$fname', lname='$lname', email='$email', explevel='$experience', addinfo='$additional', event='$regEvent' where id='$id'");

$change = "UPDATE reg_info SET fname='$fname', lname='$lname', email='$email', explevel='$experience', addinfo='$additional', event='$regEvent' where id=".$id;

$change = 'UPDATE reg_info SET fname="'.$fname.'", lname="'.$lname.'", email="'.$email.'", explevel="'.$experience.'", addinfo="'.$additional.'", event="'.$regEvent.'" where id='.$id;

从我在其他线程中看到的情况来看，至少其中一个应该对我有用。

请问谁能给我指出正确的方向吗？

如果它有帮助，整个 PHP 代码字符串是:

    <?php
$fnameErr = $lnameErr = $emailErr = $experienceErr = $regEventErr = "";
$fname = $lname = $email = $experience = $regEvent = "";
$id = $_GET["id"];
$errors = "yes";
$servername = "localhost";
$username = "root";
$password = "5tTtFzaz6dIO";
$database = "project2db";
$conn = new mysqli($servername, $username, $password, $database);
$query = mysqli_query($conn, "SELECT * FROM reg_info where id=".$id);
$row = mysqli_fetch_array($query, MYSQLI_NUM);

    if ($_SERVER["REQUEST_METHOD"] == "POST") {
     if (empty($_POST["fname"])) {
       $fnameErr = "First name is required";
       $errors = "yes";
     } else {
       $fname = test_input($_POST["fname"]);
       if (!preg_match("/^[a-zA-Z ]*$/",$fname)) {
         $fnameErr = "Only letters and white space allowed";
         $errors = "yes";
       }
       else {
        $errors = "no";
       }
     }

     if (empty($_POST["lname"])) {
       $lnameErr = "Last name is required";
       $errors = "yes";
     } else {
       $lname = test_input($_POST["lname"]);
       if (!preg_match("/^[a-zA-Z ]*$/",$lname)) {
        $lnameErr = "Only letters and white space allowed";
        $errors = "yes";
       }
       else {
        $errors = "no";
       }
     }

     if (empty($_POST["email"])) {
       $emailErr = "Email is required";
       $errors = "yes";
     } else {
       $email = test_input($_POST["email"]);
       if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $emailErr = "Invalid email address";
        $errors = "yes";
       }
       else {
        $errors = "no";
       }
     }

     if (empty($_POST["experience"])) {
       $experienceErr = "Experience level is required";
       $errors = "yes";
     } else {
       $experience = test_input($_POST["experience"]);
       $errors = "no";
     }

     if (empty($_POST["additional"])) {
       $regEvent = "";
     } else {
       $additional = test_input($_POST["additional"]);
     }

     if (empty($_POST["regEvent"])) {
       $regEventErr = "Event is required";
       $errors = "yes";
     } else {
       $regEvent = test_input($_POST["regEvent"]);
       $errors = "no";
     }

     if($errors == "no") {
        $change = 'UPDATE reg_info SET fname="'.$fname.'", lname="'.$lname.'", email="'.$email.'", explevel="'.$experience.'", addinfo="'.$additional.'", event="'.$regEvent.'" where id='.$id;
        $result=$conn->query($change);

        if ($result) {
             echo '<script language="javascript">';
             echo 'alert("New record created successfully.")';
             echo '</script>';
             header('Location: regtable.php');
        } else {
             echo '<script language="javascript">';
             echo 'alert("Error. New record not created.")';
             echo '</script>';
             header('Location: regtable.php');
        }
     }

    }

    function test_input($data) {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
    }
    ?>

Answer 1

我发现这个问题了!每当提交表单时，新的 POST 数据都没有分配给传递到 PHP 代码以创建 $id 变量的 html id="id"任何内容。

由于表单中没有任何内容，因此 $id 为 null，因此即使查询和连接完全有效，查询也不会更新数据库。

感谢所有发表评论和建议的人，我真的很感激。