根据类别从表中提取图像并停止重复的结果

Question

tables sample data

walls

wall_id   wall_name
  1        wall_1
  2        wall_2
  6        wall_6

wall_categories

wall_id   category_id
  1           2
  2           1
  6           1
  6           2

categories

category_id  category_name
  1            Wallpaper
  2            Photography

html

<a href="file.php?sort=upload_date">Date</a>
<a href="file.php?sort=wall_views">Views</a>
<a href="file.php?sort=wall_downloads">Downloads</a>

<a href="file.php?filter=1">Wallpaper</a>
<a href="file.php?filter=2">Photography</a>

php

$sortBy = array('upload_date','wall_views','wall_downloads');
$sort = 'upload_date';
if(isset($_GET['sort']) && inarray($_GET['sort'], $sortBy)){
   $sort = $_GET['sort'];
}


$filterBy = array(1, 2);
$filter = join(',', $filterBy);
if(isset($_GET['sort']) && inarray($_GET['sort'], $sortBy)){
   $sort = $_GET['sort'];
}

I'm trying to pull wall_id, wall_name, wall_views from walls table and category_name from categories table based on wall_categories table. Below is the query I got:

$walls_query = $connectDB->prepare("SELECT * FROM walls INNER JOIN wall_categories ON
                walls.wall_id = wall_categories.wall_id WHERE wall_categories.category_id  
                IN ($filter) AND walls.wall_id>? ORDER BY $sort DESC;");
     $query->execute();

and here is the query that selects the categories from database using the wall_id

$categories_query = $connectDB->prepare("SELECT category_name FROM categories INNER JOIN wall_categories 
    ON wall_categories.category_id = categories.category_id WHERE wall_id=?;");

The problem is it generates duplicate data, the images that have two categories are displayed twice. Need to stop that.