This query looks pretty odd to me in the first place, so I'm not really sure what you are going after. I doubt you really want to use UNION SELECT... you probably want to use AS to bring in those values as fields and not rows.
Unfortunately there is probably a lot for you to learn, more than I can give in a quick forum post. Do a search on the web for "inner join tutorial" to find out more about using inner joins. This example seems fairly precise and was high on my search results: forumqueue.php