我需要在数据库中更新我的数据。我在php中成功创建了用户注册和登录表单，因此我需要更新和删除数据库中的数据。我正在获取错误消息更新功能。
有条件：id（主要）和电子邮件（唯一）和用户名（唯一）。
此程序中的错误消息：
“更新记录时出错：您的SQL语法出错;请查看与您的MariaDB服务器版本对应的手册，以便在第1行附近使用正确的语法。”
<?php
session_start();
require('connect.php');
if(isset($_POST['submit'])){
$id = $_POST['id'];
$username = $_POST['username'];
$name = $_POST['name'];
$email = $_POST['email'];
$password = md5($_POST['password']);
$dob = $_POST['dob'];
$gender = $_POST['gender'];
$location = $_POST['location'];
$course = $_POST['course'];
$mobile = $_POST['mobile'];
$sql = " UPDATE user SET username ='$username', name = '$name', email = '$email', password='$password', dob ='$dob', gender ='$gender',location ='$location', course = '$course', mobile = '$mobile' WHERE id= $id ";
if (mysqli_query($mysqli, $sql)) {
$smsg = "Record updated successfully";
} else {
$fmsg = "Error updating record: " . mysqli_error($mysqli);
}
}
?>
<html>
<head>
<title>User Update PHP & MYSQL</title>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" >
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap-theme.min.css" >
<link rel="stylesheet" href="main.css" >
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<a class= "float-right" href = "logout.php"> LOGOUT </a>
<?php if(isset($smsg)){ ?><div class="alert alert-success" role="alert"> <?php echo $smsg; ?> </div><?php } ?>
<?php if(isset($fmsg)){ ?><div class="alert alert-danger" role="alert"> <?php echo $fmsg; ?> </div><?php } ?>
<form class="form-signin" method="POST">
<h2 class="form-signin-heading">Edit Profile</h2>
<div class="input-group">
<input type="hidden" name="id" placeholder="ID">
<input type="text" name="username" class="form-control" placeholder="username" required></div>
<label for="inputname" class="sr-only">Full Name</label>
<input type="text" name="name" id="inputname" class="form-control" placeholder="Full Name"required>
<label for="inputEmail" class="sr-only">Email address</label>
<input type="email" name="email" id="inputEmail" class="form-control" placeholder="Email address"required>
<label for="inputPassword" class="sr-only">Password</label>
<input type="password" name="password" id="inputPassword" class="form-control" placeholder="Password" required>
<label for="inputDoB" class="sr-only">DOB</label>
<input type="date" name="dob" id="inputDoB" class="form-control" placeholder="DOB"required>
<td>Gender:</td>
<input type="radio" name="gender" value="m">Male
<input type="radio" name="gender" value="f">female
</tr>
<label for="inputlocation" class="sr-only">Location</label>
<input type="text" name="location" id="inputlocation" class="form-control" placeholder="Location"required>
<label for="inputcourse" class="sr-only">Course</label>
<input type="text" name="course" id="inputcourse" class="form-control" placeholder="Course" required>
<label for="inputmobile" class="sr-only">Mobile</label>
<input type="text" name="mobile" id="inputmobile" class="form-control" placeholder="Mobile" required>
<button class="btn btn-lg btn-primary btn-block" type="submit" name="submit">Update</button>
</div>
</body>
</head>
</html>
你还没有为id增加价值。
它是一个隐藏变量，因此，它只能通过PHP或JS设置，而不能通过用户输入。
因此，您的查询在where子句为空并导致错误之后。
解：
为id分配一个值。
<input type="hidden" name="id" placeholder="ID" value="<?php echo $user_id;?>">
要避免此错误，请检查是否已发布id。
修改：
if(isset($_POST['submit'])) {
至：
if(isset($_POST['submit']) && ! empty($_POST['id'])){