SQL - How To Order Using Count From Another Table

Question

1. Bloggers

blogger_id
1 
2
3

2. Posts

post_from_blogger_id
1 
1
1
2
2
3

As

Answer 1

Try this:

SELECT B.blogger_id,
       B.blogger_name,
       IFNULL(COUNT(P.post_from_blogger_id ),0) AS NumPosts 
From Blogger AS B
LEFT JOIN Posts AS P ON P.post_from_blogger_id = B.blogger_id
GROUP BY B.blogger_id, B.blogger_name
ORDER BY COUNT(P.post_from_blogger_id ) DESC

This joins the 2 tables, and counts the number of entries in the Posts table. If there are none, then the count is 0 (IFNULL).