title: WordPress - producing a list of posts filtered by tag and then category
body: <p>I'm trying to make a WordPress site that has six lists on a page, each list showing posts from a different category. Simple.</p>
  
  <p>But then, if a user selects a tag, taking them to that tag archive page, I want them to still see the six-list template, but all the posts within each category are also filtered by the tag. So lists of posts are filtered first by tag, and then by category.</p>
  
  <p>As far as I can tell, there is no way of doing this using query_posts or anything, it needs more advanced use of the database, but I have no idea how to do this! I think that there's a similar question on here, but because I know very little PHP and no MySQL, I can't make sense of the answers!</p>