Each Article can have unlimited categories.
Categories are saved in the database like this
example article_category: '1','3','8'
OR
example article_category: '2','3'
So when I search for a listing under, lets say category 3
$category_id = $_REQUEST['category_id']; //3
$SQL = "SELECT * FROM ARTICLES WHERE article_category = '$category_id'";
If it were just one the above would work fine.
I hate to say it but I'm completely lost.. Would I use IN ?
$_REQUESTdirectly in your SQL query. You should escape them or use PDO.