我制作了一个让人们互相关注的php文件

I made this PHP page to let people follow each other it takes the following user id from the table users and when the logged-in user presses follow, the action should be saved in followers table.

followers table
    id  int
    user_id int
    follower-id int

users table
    email varchar
    id int
    username varchar
    password varchar

I am getting this error

:Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42S22]: Column not found: 1054 Unknown column 'follower' in 'field list'' in C:\socialnetwork\classes\DB.php:12 Stack trace: #0 C:socialnetwork\classes\DB.php(12): PDOStatement->execute(Array) #1 C:\Users\Karim\Desktop\socialnetwork\profile.php(17): DB::query('SELECT follower...', Array) #2 {main} thrown in C:socialnetwork\classes\DB.php on line 12

Thank you for your time.

<?php
include('./classes/DB.php');
include('./classes/Login.php');
$username = "";

if (isset($_GET['username'])) {
        if (DB::query('SELECT username FROM users WHERE username=:username', array(':username'=>$_GET['username']))) {
                $username = DB::query('SELECT username FROM users WHERE username=:username', array(':username'=>$_GET['username']))[0]['username'];
                if (isset($_POST['follow'])) {



                        $userid = DB::query('SELECT id FROM users WHERE username=:username', array(':username'=>$_GET['username']))[0]['id'];
                        $followerid = Login::isLoggedIn();


                        if (!DB::query('SELECT follower-id FROM `followers` WHERE user_id=:user_id', array(':user_id'=>$userid))) {
                                DB::query('INSERT INTO followers VALUES (null, :user_id, :follower-id)', array(':user_id'=>$userid, ':follower-id'=>(int)$followerid));
                        } else {
                                echo 'Already following!';
                        }
                }
        } else {
                die('User not found!');
        }
}
?>

<h1><?php echo $username; ?>'s Profile</h1>
<form action="profile.php?username=<?php echo $username; ?>" method="post">
        <input type="submit" name="follow" value="Follow">
</form>

Hyphens, even though not disallowed, can cause problems in column names.

In order to make it work you have to enclose the name of the column with back-ticks:

SELECT `follower-id` FROM

As MySQL documentation confirms:

Permitted characters in unquoted identifiers:

ASCII: [0-9,a-z,A-Z$_] (basic Latin letters, digits 0-9, dollar, underscore)

Extended: U+0080 .. U+FFFF

Permitted characters in quoted identifiers include the full Unicode Basic Multilingual Plane (BMP), except U+0000:

ASCII: U+0001 .. U+007F

Extended: U+0080 .. U+FFFF

ASCII code for dash - is 45, which is within the "quoted identifiers" ASCII range