Question

I am trying to convert Xoops posts to WordPress. As part of that, I want to get comment count for a topic. Post and replies are on same “topic_id”. How to count them and post it in to new column?

DB current status

topic_id | subject             |comment_count|
+________+_____________________+_____________+
1    | welcome             | 
1    | Re: welcome         |
2    | hello world         |
2    | Re: hello world     |
2    | Re: hello world     |
3    | hello friends       |

from here I want to take the (count of topic_id – 1) as the number of replays (comment count). Guide me to query in MYSQL

I want to place the output in the same table. (comment_count)

DB expected output

   | topic_id | subject             |comment_count|
   +________+_____________________+_____________+
   | 1   | welcome             | 1 
   | 1   | Re: welcome         | 1
   | 2   | hello world         | 2
   | 2   | Re: hello world     | 2
   | 2   | Re: hello world     | 2
   | 3   | hello friends       | 0

Answer 1

    select *,t2.comment_count  from table t1 
     join
     (
       select count(*),CONCAT('Re', ' ', subject) 
        as replay,topic_id as comment_count 
        from table 
        where suject=replay group by topic_id
     ) as t2 on t1.topic_id=t2.topic_id