A function with one parameter

<?php
  function get_products_by_category($category_id) {
    global $db;
    $query = 'SELECT * FROM products
              WHERE products.categoryID = :category_id
              ORDER BY productID';
    $statement = $db->prepare($query);
    $statement->bindValue(':category_id', $category_id);
    $statement->execute();
    $products = $statement->fetchAll();
    $statement->closeCursor();
    return $products; // returns an array of products
  }
?>