Question

Setup as below works.
But, what I want to achive is to count how many rows there is in BlogComment where BlogComment.BlogPostId = BlogPost.BlogPostId.

Anyone got suggestion ?

SELECT * FROM BlogPost
INNER JOIN BlogUser
ON BlogPost.BlogUserId = BlogUser.BlogUserId
INNER JOIN Category
ON BlogPost.CategoryId = Category.CategoryId
INNER JOIN BlogComment
ON BlogPost.BlogPostId = BlogComment.BlogPostId
Order By BlogPost.BlogPostId Desc

Answer 1

If you want all the data plus a count (as opposed to just the count) you can create an inline query in the from clause to do this.

SELECT *, 
       COALESCE(c.count_post_id,0) as count_post_id
FROM   blogpost 
       INNER JOIN bloguser 
         ON blogpost.bloguserid = bloguser.bloguserid 
       INNER JOIN category 
         ON blogpost.categoryid = category.categoryid 
       LEFT JOIN (SELECT blogpostid, 
                          COUNT(blogpostid) count_post_id
                   FROM   blogcomment
                   GROUP BY blogpostid) c
         ON c.blogpostid = blogpost.blogpostid 
ORDER  BY blogpost.blogpostid DESC 

Some RDMS give additional options like using CTEs or Cross Apply