ISSUE USE ORDER BY AND LIMIT IN PHP

<?php 
include("inc/functions.php");
$pageTitle = "Personal Media Library";
$section = null;

include("inc/header.php"); ?>
        <div class="section catalog random">

            <div class="wrapper">

                <h2>May we suggest something?</h2>

        <ul class="items">
            <?php
            $random = random_catalog_array();
            foreach ($random as $item) {
                echo get_item_html($item);
            }
            ?>                          
                </ul>

            </div>

        </div>

<?php include("inc/footer.php"); ?>

<?php 
include("inc/functions.php");
$catalog = full_catalog_array();

$pageTitle = "Full Catalog";
$section = null;

if (isset($_GET["cat"])) {
    if ($_GET["cat"] == "books") {
        $pageTitle = "Books";
        $section = "books";
    } else if ($_GET["cat"] == "movies") {
        $pageTitle = "Movies";
        $section = "movies";
    } else if ($_GET["cat"] == "music") {
        $pageTitle = "Music";
        $section = "music";
    }
}

include("inc/header.php"); ?>

<div class="section catalog page">

    <div class="wrapper">

        <h1><?php 
        if ($section != null) {
            echo "<a href='catalog.php'>Full Catalog</a> &gt; ";
        }
        echo $pageTitle; ?></h1>

        <ul class="items">
            <?php
            $categories = array_category($catalog,$section);
            foreach ($categories as $id) {
                echo get_item_html($catalog[$id]);
            }
            ?>
        </ul>

    </div>
</div>

<?php include("inc/footer.php"); ?>

<? function random_catalog_array() {
  include("connection.php");
  try{
  $results = $db->query("SELECT media_id, title,category,img
            FROM Media
            ORDER BY RAND()
            LIMIT 4"
          );
   } 
    catch(Exception $e){
    echo "Unable to retrieved results";
    exit;
    }
    $catalog=$results->fetchAll();
    return $catalog;
} ?>