Question

i have got lot of queries which are written like:

     select  thread_id as topic_id,title as topic            
  ,            
    isnull((select count(*) from tblmessages b where thread_id=a.thread_id and is_approved='Y' and sort_level>1            
     group by b.thread_id            
     ),0) as replies,            
    isnull((select count(*) from tblmessages b where thread_id=a.thread_id and isnull(new_post,'Y')='Y' and sort_level>1            
     group by b.thread_id            
     ),0) as NewPost,            
    isnull((select count(*) from tblmessages b where thread_id=a.thread_id and isnull(is_approved,'N')='N' and sort_level>1            
     group by b.thread_id            
     ),0) as NotClear,            

    sort_level,sort_index,  from tblMessages a            
    where   sort_level=1 and category=@category 
    order by topic_id desc

Please tell me how to optimize and better way to write such queries. because i have got tables with records 5,00,000. so it takes lots of time and some times gets time out.

Thanks

Answer 1

You should group the variuos subquery in a single one with different count and use a join to put the data together

the subquery should be:

select thread_id
     count(when isnull(is_approved,'N')='N' then 1 end) as replies,
     count(when isnull(new_post,'Y')='Y' then 1 end) as NewPost,
     count(when isnull(is_approved,'N')='N' then 1 end) as NotClear
     from tblmessages 
     where sort_level>1  
     group by thread_id

While the finalquery is the following

select  thread_id as topic_id,title as topic,
   sort_level,sort_index , B.replies, B.NewPost, B.NotClear
   from tblMessages a            
   join
     (select thread_id
     count(when isnull(is_approved,'N')='N' then 1 end) as replies,
     count(when isnull(new_post,'Y')='Y' then 1 end) as NewPost,
     count(when isnull(is_approved,'N')='N' then 1 end) as NotClear
     from tblmessages 
     where sort_level>1  
     group by thread_id) as B
     on a.thread_id = B.thread_id
    where   sort_level=1 and category=@category 
    order by topic_id desc