php - 如何获得问题表中未回答的问题？

Question

我有两个表

question
------------------------------
qid  |  qname  |  description
------------------------------
1      ssc?       blabla

2      BIE        blabla

3      msc        blabla

answer
----------------------------
aid  | uid  | qid | answered_on
-------------------------------
1      1      1     ssc means

2      2      1     ssc
-------------------------------

现在我想得到未回答的问题如何编写查询？你能告诉任何人吗。

i get the result like 

qid | qname
-----------
2     BIE
3     msc

Answer 1

select * from  users as ru left join answers as ra on ru.uid=ra.uid 
left join questions as rq on rq.uid=ru.uid 
where   rq.qid not in(select qid from answers) group by rq.qid order by rq.qid desc

如果你有一个用户表，这可能很有用，检查一下