คะแนนคำตอบเฉลี่ยสำหรับผู้ใช้ทุกคน ไม่จำเป็นต้องใช้ทุกตาราง
Average answer score for all users.It is not neccessary to use all the tables.
 PostLinks:  Id [ number]  CreationDate [ time]  PostId [ number]  RelatedPostId [ number]  LinkTypeId [ number] 
SELECT u.DisplayName, COUNT(1) AS answers_count, SUM(a.Score) AS total_score, SUM(a.Score) * 1.0 / COUNT(1) AS avg_score FROM Users AS u JOIN Posts AS a ON u.Id = a.OwnerUserId AND a.PostTypeId = 2 GROUP BY u.Id, u.DisplayName ORDER BY avg_score DESC, answers_count DESC