SQL Update error. Instead of updating, its adding. : //for some reason it won't update, instead it will add the new data. 
I am a beginner, and I have hard time trying to find out the error. 
Thank you for the help.     
//Read function was working very properly and insert works just fine as well. Its just the update that doesnt work properly, or inserts instead of updating the query or data. 
<?php include "db.php"; ?>
    
    <?php include "functions.php" ?>
    
    <?php
    
    if(isset($_POST['submit']))
    
    {$username = $_POST['username'];
        
        $password = $_POST['password'];
        
        $id = $_POST['id'];
        
        $querys = "UPDATE users SET ";
        
    $querys .= "username = '$username', ";
        
    $querys .= "password = '$password' ";
        
    $querys .= "WHERE id = $id ";
    
        
    $result = mysqli_query($connection, $querys);
        
    if(!$result)
        {
            die('Query FAILED'. mysqli_error($connection));
        }
    }
    
    ?>
    
    <!DOCTYPE html>
    
    <html lang="en">
    
    <head>
    
        <meta charset="UTF-8">
    
        <title>Document</title>
        
    
    <link rel="stylesheet" 
    
    href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css
    
    ">
    
    </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
                 showAllData();
                ?>
                
                </select>
                </div>
                
                <input class="btn btn-primary" 
                type="submit" name="submit" value="Update">
            </form>    
            
        
        </div>
    </div>
    </body>
    </html>