我正在从数据库中检索值以进行更新，在按下提交按钮时，值应该会更新。
代码如下：
PostUpdate.php：
<?php
session_start();
$username=$_SESSION['uname'];
$cn=mysqli_connect("localhost", "root", "", "testdb");
// Define variables and initialize with empty values
$course = $category = "";
$title = $descp = "";
// Processing form data when form is submitted
if(isset($_POST["pid"]) && !empty($_POST["pid"])){
// Get hidden input value
$pid = $_POST["pid"];
// Check input errors before inserting in database
if(empty($course) && empty($category) && empty($title) && empty($descp)){
// Prepare an update statement
$sql = "UPDATE posts SET course=?, category=?, title=?, descp=? WHERE pid=?";
if($stmt = mysqli_prepare($cn, $sql)){
// Bind variables to the prepared statement as parameters
mysqli_stmt_bind_param($stmt, "ssssi", $param_course, $param_category, $param_title, $param_descp, $param_pid);
// Set parameters
$param_course = $course;
$param_category = $category;
$param_title = $title;
$param_descp = $descp;
$param_pid = $pid;
// Attempt to execute the prepared statement
if(mysqli_stmt_execute($stmt)){
// Records updated successfully. Redirect to landing page
header("location: CAposts.php");
exit();
} else{
echo "Something went wrong. Please try again later.";
}
// Close statement
mysqli_stmt_close($stmt);
}
}
// Close connection
mysqli_close($cn);
} else{
// Check existence of id parameter before processing further
if(isset($_GET["pid"]) && !empty(trim($_GET["pid"]))){
// Get URL parameter
$pid = trim($_GET["pid"]);
// Prepare a select statement
$sql = "SELECT * FROM posts WHERE pid = ?";
if($stmt = mysqli_prepare($cn, $sql)){
// Bind variables to the prepared statement as parameters
mysqli_stmt_bind_param($stmt, "i", $param_pid);
// Set parameters
$param_pid = $pid;
// Attempt to execute the prepared statement
if(mysqli_stmt_execute($stmt)){
$result = mysqli_stmt_get_result($stmt);
if(mysqli_num_rows($result) == 1){
/* Fetch result row as an associative array. Since the result set contains only one row, we don't need to use while loop */
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
// Retrieve individual field value
$pid = $row['pid'];
$uname = $row['uname'];
$course = $row['course'];
$category = $row['category'];
$pdate = $row['pdate'];
$title = $row['title'];
$descp = $row['descp'];
} else{
// URL doesn't contain valid id. Redirect to error page
header("location: CAposts.php");
exit();
}
} else{
echo "Oops! Something went wrong. Please try again later.";
}
}
// Close statement
mysqli_stmt_close($stmt);
// Close connection
mysqli_close($cn);
} else{
// URL doesn't contain id parameter. Redirect to error page
header("location: CAposts.php");
exit();
}
}
?>
<html>
<head>
<title>IMEDTalks-Post-
<?php echo $title;?>
</title>
<link href="./css/bootstrap.min.css" rel="stylesheet" />
<script src="./scripts/jquery-3.3.1.min.js"></script>
<script src="./scripts/bootstrap.min.js"></script>
<style>
/* Make the image fully responsive */
.carousel-inner img {
width: 100%;
height: 30%;
}
</style>
</head>
<body>
<div class="wrapper">
<div class="container-fluid">
<div class="row">
<div class="col-md-12">
<div class="page-header">
<h2 class="text-center">Update Post</h2>
</div>
<p class="text-center">Please edit the input values and submit to update the post.</p>
<form action="<?php echo htmlspecialchars(basename($_SERVER['REQUEST_URI'])); ?>" method="post">
<div class="form-group">
<div class="row">
<label class="col-form-label col-md-1 offset-3" for="course">Course:</label>
<div class="col-md-2">
<select name="course" class="form-control" required>
<option value="<?php echo $course;?>" selected>
<?php echo $course;?>
</option>
<option value="">Choose any:</option>
<option value="comp">Comp</option>
<option value="theo">Theory</option>
</select>
</div>
<label class="col-form-label col-md-1" for="category">Category:</label>
<div class="col-md-3">
<select name="category" class="form-control" required>
<option value="<?php echo $category;?>" selected>
<?php echo $category;?>
</option>
<option value="">Choose any:</option>
<option value="plang">Programming Language</option>
<option value="web">Web Technologies</option>
<option value="maths">Mathematics and Statistics</option>
<option value="others">Others</option>
</select>
</div>
</div>
</div>
<div class="form-group row">
<label for="title" class="col-form-label col-md-2">Title:
</label>
<div class="col-md-10">
<input type="text" class="form-control" value="<?php echo $title;?>" name="title" required>
</div>
</div>
<div class="form-group row">
<label for="desc" class="col-form-label col-md-12">Description:
</label>
<div class="col-md-12">
<textarea class="form-control" name="descp" rows="20" required><?php echo $descp;?></textarea>
</div>
</div>
<input type="hidden" name="pid" value="<?php echo $pid;?>" />
<div class="form-group row">
<div class="col-md-4 offset-4">
<a href="CAposts.php"><button type="button" name="cancel"
class="btn-lg btn-danger">Cancel</button></a>
</div>
<div class="col-md-4">
<button type="submit" name="update" class="btn-lg btn-success">Submit</button>
</div>
</div>
</form>
</div>
</div>
</div>
</div>
</body>
</html>
在这里，我使用的是pid，该pid是从上一页（以表格格式列出数据）购买的，然后单击那里的按钮，该数据/帖子就会加载到表单中以进行编辑和更新使用pid（数据库表中的主键） 我使用引导程序4。
我面临的问题：
使用pid进行更新操作没有任何错误，但是在执行此更新操作后，数据库表中的课程，类别，标题，描述的值将设置为空白。
我不知道这里出了什么问题。