无法找出一个SQL查询来关联两个表

Question

Ok, I have two tables.

Table 'topic'

tid | posts 
------------
1       4
3       2

Table 'posts'

topic_id |  post
-----------------
1      xxxx
3      aaaa
1      dddd
1      ddsdss
3      rreer
1      gsdsd

My abstract query is like this:

select counter(*) as c 
from posts as p, topic as t 
where p.tid = t.topicid 
  and c != t.posts

This should return counter of all 'posts' table rows which matches with 'topic' table tid and also does not matche with Table 'topic' posts count.

Also I need to update the colum "posts" of topic with the counter(*) value if found different.

update topic set posts = (SELECT COUNT(*) from posts WHERE posts.topicid = topic.tid and topic.posts <> (SELECT COUNT(*) from posts WHERE posts.topicid = topic.tid))

I tried many ways to get this working, but could not figure out. Would really appreciate if anyone can explain a query for this case ?

---

Actually what I am trying do is this. I want to update posts counter of topic for all the matching topic ids between table if posts count of 'posts' table does not match 'topic' table posts counter. You get me ? I tried to play with your query, but it does other way of giving me 'topic' table rows instead which is not I want.

UPDATE topics SET posts = (
  SELECT COUNT(*) 
  FROM posts 
  WHERE topicid = (
    SELECT tid 
    FROM topics 
    WHERE topics.tid = topicid
 ) 
 GROUP BY topicid HAVING COUNT(*) <> (
   SELECT posts 
   FROM topics WHERE topics.tid = topicid
 )
) **WHERE tid = (
  SELECT topicid 
  FROM posts 
  WHERE topicid = (
    SELECT tid 
    FROM topics 
    WHERE topics.tid = topicid
  ) GROUP BY topicid HAVING COUNT(*) <> (
      SELECT posts FROM topics WHERE topics.tid = topicid
  )
)**

Answer 1

The following will give you the topic and count

If you want to find the topics that are "wrong" then join this to the the count table

SELECT *
FROM topic
LEFT JOIN (
  SELECT topic_id, count(*) as t_count
  FROM posts
  GROUP BY topic_id
) sub on topic.tid  = sub.topic_id

Then to see the ones that are different you can add a where

WHERE topic.posts <> sub.t_count