An Error Was Encountered

Error Number: 1064

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 'AND threads.date < NOW() AND threads.closed=0 AND threads.published=1 AND thread' at line 1

SELECT *, threads.id AS thrid FROM users, threads WHERE threads.category = AND threads.date < NOW() AND threads.closed=0 AND threads.published=1 AND threads.users_id = users.id