Question regarding PHP

I'm getting an error that reads:

" Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in /home/user/public_html/iwd/productDetail.phpon line 26"

My code is below

'includes/header.html.php'; ?>  
role="main" class="inner cover"> 
class="cover-heading">Album Details
 id="example" class="table table-bordered table-hover">  //include database conncection  require_once('includes/mysqli_connect.php'); $AlbumId = isset($_GET['AlbumId']) ? $_GET['AlbumId'] : ' '; $sql = "SELECT Album.AlbumId, Artist.Name, Album.Title, Track.Name, Track.UnitPrice, Genre.Name FROM `Album` INNER JOIN `Artist` ON Album.ArtistId = Artist.ArtistId INNER JOIN `Genre` ON Album.ArtistId = Genre.GenreId INNER JOIN `Track`ON Album.AlbumId = Track.AlbumId INNER JOIN `MediaType` ON Track.MediaTypeId = MediaType.MediaTypeId WHERE AlbumId = '$AlbumId'"; //execute the query  $results = mysqli_query($db, $sql); $Album = mysqli_fetch_array($results); ?>  
$Album['AlbumId'] ?>
$Album['Name'] ?>
$Album['Title'] ?>
$Album['Name'] ?>
$Album['UnitPrice'] ?>
$Album['Name'] ?>
 
 'includes/footer.html.php'; ?>