How can i display my SELECT data correctly in PHP website?

My database is working fine, but i am facing problems using the data and display them in my site.php

So in my config.php file, i have the following code:

<?php
/* Database credentials. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
define('DB_SERVER', 'localhost');
define('DB_USERNAME', 'root');
define('DB_PASSWORD', '');
define('DB_NAME', 'xxx');
 
/* Attempt to connect to MySQL database */
$link = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD, DB_NAME);
 
// Check connection
if($link === false){
    die("ERROR: Could not connect. " . mysqli_connect_error());
}
?>

In my site.php i am using the following code:

        <?php

        $sql = "SELECT * FROM dish";

        $res = mysqli_query($link, $sql);

        ?>
            <div class="col-md-3">
                <div class="thumbnail">
                    <a href="index.php">
                        <img src="img/gallery/01.jpg" class="rounded-top">
                    </a>
                    <h4 class="text-center my-3"><?php echo $nom ?></h4>
                    <p class="text-center"><?php echo $description ?></p>
                    <a href="index.php?dish_did<?php echo $did; ?>" class="btn btn-success" role="button">Rate Now!</a>
                </div>
            </div>

In my localhost site.php i get the following error

Warning: Undefined variable $link in C:\xampp\htdocs\Version\site.php on line 39

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in C:\xampp\htdocs\Version\site.php:39 Stack trace: #0 C:\xampp\htdocs\Version\site.php(39): mysqli_query(NULL, 'SELECT * FROM d...') #1 {main} thrown in C:\xampp\htdocs\Version\site.php on line 39

line 39 is this:

$res = mysqli_query($link, $sql);

How can i fix this and use my database correct in PHP?

>Solution :

It seams like you are not using any framework, so if that is true, you need to add an include statement at the top of your site.php, something like this

<?php require 'config.php'; ?>

so that the config.php file is executed before the content of your site.php file is.

however, I must add that ( beyond didactic purposes ) what you are doing is not a good practice. It would be better to use a framework like "laminas" or any other, that allows you do Separation of concerns, Dependency injection, Inversion of Control, etc.