How to JOIN a COUNT from a table, and then effect that COUNT with another JOIN

Question

I have three tables

Post

ID  Name
1   \'Something\'
2   \'Something else\'
3   \'One more\'

Comment

ID  PostId  Profile         


        

Answer 1

From the definition of the COUNT function:

The COUNT function will only count those records in which the field in the brackets is NOT NULL.

This means that simple outer join like this would work:

SELECT Post.ID, COUNT(Comment.ID)
  FROM Post LEFT JOIN Comment ON (Post.ID = Comment.PostId)
            LEFT JOIN Profile ON (Profile.ID = Comment.ProfileID AND
                                  Profile.Approved = 1)
 GROUP BY Post.ID