我也看到过类似的主题，但是在尝试了上面提到的一些解决方案之后，我仍然没有找到正确的答案。我是mysql和php的新手，我很确定在某个地方有一个我看不到的小错误，但是我已经为这个问题挣扎了几天了，所以我决定问一下。
问题是，当我创建一个html表单和方法将表单中的值插入数据库时，我得到了“成功”的插入，但是添加到数据库中的所有行仍然是空的。
html表单：

<div class="panel panel-default">
<div class="panel-body">
<form action="InsertMessage.php" method="post">
    <div class="form-group">
        <label for="comment">First name:</label>
        <textarea class="form-control" id="comment" name=first_name rows="1" required></textarea>
    </div>
    <div class="form-group">
        <label for="email">Email address:</label>
        <input type="email" class="form-control" name="email" id="email" required>
    </div>
    <div class="form-group">
        <label for="date">Date:</label>
        <input type="date" class="form-control" name="desired_date" id="desired_date" required>
    </div>
    <div class="form-group">
        <label for="time">Time:</label>
        <input type="time" class="form-control" name="desired_time" id="desired_time" required>
    </div>
    <div class="form-group">
        <label for="comment">Comment</label>
        <textarea class="form-control" id="comment" name="info" rows="3" placeholder="placeholder" required></textarea>
    </div>
    <button type="submit" class="btn btn-default">Submit</button>
</form>
</div>
</div>

php代码：

$host = "localhost";
$username = "root";
$password = "";
$database = "name";

//create a connection

$conn = new mysqli($host, $username, $password, $database);

$first_name = filter_input(INPUT_POST, 'first_name');
$email = filter_input(INPUT_POST, 'email');
$desired_date = filter_input(INPUT_POST, 'desired_date');
$desired_time = filter_input(INPUT_POST, 'desired_time');
$info = filter_input(INPUT_POST, 'info');

if(mysqli_connect_error()){
    die('Connection error (' . mysqli_connect_errno() . ')' . 
mysqli_connect_error());
}else{
    $sql = "INSERT INTO messages (first_name, email, desired_date,  
desired_time, info) VALUES 
('$first_name','$email','$desired_date','$desired_time','$info')";
    if ($conn->query($sql)){
        echo "New record is inserted successfully!";
    }
    else{
        echo "Error:" . $sql . $conn->error;
    }
    $conn->close();
}

phpmyadmin截图：