[Xenon]

well, somewhere in your script you define the $threads variable:

$threads=$DB_site->query("SELECT * FROM thread WHERE ...

to use a join query you have to chang it into this:

$threads=$DB_site->query("SELECT thread.*,reqdata.* FROM thread LEFT JOIN reqdata USING(threadid) WHERE ...

then you don't need the query in th while loop anymore, you can acces to all data within reqdata table throug $thread variable