PHP MySql:为什么我的选择选项不显示下拉列表中的数字?

Why does my select option not display the number in the dropdown select? What's wrong?

<?php
$query = "SELECT * FROM users";
$result = mysqli_query($mysqli, $query);
    if(!$result){
      die('Query FAILED');
}
?>
  <!DOCTYPE html>
  <html>
  <head>
    <meta charset="utf-8">

  </head>
  <body>
   <div class="container">
      <div class="col-xs-6">

      <form action="login_create.php" method="post">
        <div class="form-group">
            <label for="username">Username</label>
            <input type="text" name="username" class="form-control"/>
        </div>
        <div class="form-group">
            <label for="password">Password</label>
            <input type="password" name="password" class="form-control">
        </div>
          <div class="form-group">
            <select name="id" id = " ">
                            <?php
                            while($row = mysqli_fetch_assoc($result)){
                                  $id = $row['id'];
                              echo "<option value='$id'>$id</option>";
                            }
                            ?>
            </select>
          </div>
        <input class="btn btn-primary" type="submit" name="submit" 
value="UPDATE">
         </form>
  </div>
</div>
</body>
</html>

Are you connected to the DB, what's this value

$mysqli

It's never defined/set in your post. Therefore I have to assume you never connected to the DB.

First place to start always, is turn on error reporting

<?php
     ini_set('display_errors', 1);
     error_reporting(-1); //or E_ALL
     ... other code ...

If you do that and it says, something like.

Warning undefined variable $mysql

Then you will know.

You must call Database connection...

Replace

  1. LOCALHOST with your host (For WAMP/XAMPP: localhost)
  2. USERNAME with Database username (For WAMP/XAMPP: root)
  3. PASSWORD with Database Password (For WAMP/XAMPP: )[Blank]
  4. DATABASE with Database name

    $mysqli = new mysqli('LOCALHOST','USERNAME','PASSWORD','DATABASE')
    
    $query = "SELECT * FROM users";
    
    $result = mysqli_query($mysqli, $query);
    
    if(!$result){
    
        die('Query FAILED');
    
    }