Help with LEFT JOIN command in php & mysql

What I wanna do is replace ALL columns in the "subject" field & that has a "0" in "replyto" with the subject ( as long as it is 0) because when replying it leaves a "RE" thing which i dont like... so i just wanna replace it with the subject matching 0

How can I accomplish this??

$result = mysql_query("
  SELECT * FROM mybb_posts 
    LEFT JOIN 开发者_如何学编程mybb_userfields ON (mybb_posts.uid = mybb_userfields.ufid) 
  WHERE (fid=42) OR (replyto=0) 
  ORDER BY pid DESC 
  LIMIT 0,3
");

http://img444.imageshack.us/img444/4964/helpoi.jpg

You can see in the yellow-ish picture that i pull the information successfully and the crossed out subject is what i am talking about

The table in the picture is the "mybb_posts" table

I'm not familiar with MyBB, but is the "RE:" included on the front-end? Or does it actually come from the database. The reason I ask is that it may only require a simple edit to the front-end file to remove the "RE:" rather than trying to modify the SQL query itself.