MySQL Error

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ORDER BY id DESC LIMIT 15' at line 2
Querystring
SELECT f_posts.topicId, f_posts.id, f_posts.topicId as address, f_posts.editDate, f_posts.crDate, f_posts.text, f_posts.author, f_posts.authorId, f_topics.title 
		FROM f_posts INNER JOIN f_topics ON f_topics.id = f_posts.topicId WHERE topicId =  ORDER BY id DESC LIMIT 15