How can I include more query in one query?

These are my tables:

tbl_answers => 
  aid     
  qid     
  answer     
  uid     
  dateposted     
  emailnotify
  namedisplay
  status
  isbestanswer 


tbl_questions =>
  qid
  question
  detail
  mcid
  cid
  uid     
  answercount
  dateposted
  status
  showname
  emailnotify
  question_type_id  

I woud like to update those question that has got more answers than it’s counted in:
tbl_questions => answercount

How can I update the rows which have got more questions than it’s counted? (Without php loop)

This is how I’m trying now:

UPDATE tbl_questions
  JOIN (
    SELECT tbl_questions.qid, COUNT(*) AS n 
    FROM tbl_questions JOIN tbl_answers ON tbl_answers.qid = tbl_questions.qid 
    WHERE answercount = "0" 
    GROUP BY id
  ) AS T USING (tbl_answers.qid)
SET answercount = n 
WHERE n > 0

IT says me 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 '.qid) SET answercount = n WHERE n > 0' at line 7

Wouldn’t this be sufficient for your update, since the subquery providing the update value evaluates to 0 if there aren’t any answers for your question.

UPDATE tbl_questions q
SET q.answercount = (SELECT COUNT(*) FROM tbl_answers a WHERE a.qid = q.id)
WHERE q.answercount = 0