PHP sorting database items with ORDER BY query MySQL

I have a MySQL database with which I'm dynamically populating a web page. I'm building a MySQL query that fetches some products stored in a table called `products` that I can later echo out on the page with PHP. The columns in that table are `id`, `product_name`, `price` and `description`. I want the user to be able to sort products alphabetically, by price (low-high) etc by clicking the relevant links on the page. This is what I've written so far: ``` // Run a SELECT query to get all the products stored in the database // By default, if no sorting URL variable is fed into the page, then the SQL query becomes order by id. // The first time you land on the index page as plain index.php, not index.php?=variable, this is the query that's used $sql = mysqli_query($con,"SELECT * FROM products ORDER BY id DESC"); // If the user chooses to sort the produts in a different way, then an HTML link will set a PHP variable into this page // We will check for that variable and change the SQL query to sort the products in a different way if (isset($_GET['sortby'])) { // Capture that in a variable by that name $sortby = $_GET['sortby']; // Now to change the SQL query based on the sorting the user chose (price high to low, low to high, alphabetical and latest first) if ($sortby = 'pricehilo') { $sql = mysqli_query($con,"SELECT * FROM products ORDER BY price DESC"); } elseif ($sortby = 'pricelohi') { $sql = mysqli_query($con,"SELECT * FROM products ORDER BY price ASC"); } elseif ($sortby = 'name') { $sql = mysqli_query($con,"SELECT * FROM products ORDER BY product_name"); } } ``` The page is `index.php`, and these are the links in the HTML: ``` <p><a href="index.php?sortby=pricehilo">Price (Highest-Lowest)</a></p> <p><a href="index.php?sortby=pricelohi">Price (Lowest-Highest)</a></p> <p><a href="index.php?sortby=name">Alphabetical</a></p> ``` When I load the page for the first time, all my products are displayed sorted by ID. However, when I click on any link, the products get sorted by price highest to lowest. If I refresh the page as just index.php the products remain sorted by price highest to lowest - the SQL query it is taking is that. How can I fix this?