คะแนนเฉลี่ยเป็นฟังก์ชันของชั่วโมงของวัน ไม่จำเป็นต้องใช้ตารางทั้งหมด
Mean score as function of hour of the day.It is not neccessary to use all the tables.
 CloseReasonTypes:  Id [ number]  Name [ text]  Description [ text] 
SELECT TIME_TO_STR(a.CreationDate, '%I') AS answerhour, TIME_TO_STR(q.CreationDate, '%I') AS questionhour, AVG(1.00 * a.Score) AS score FROM Posts AS a JOIN Posts AS q ON q.Id = a.ParentId WHERE a.PostTypeId IN (2) AND TIME_TO_STR(q.CreationDate, '%Y') = 2018 GROUP BY TIME_TO_STR(a.CreationDate, '%I'), TIME_TO_STR(q.CreationDate, '%I') ORDER BY TIME_TO_STR(a.CreationDate, '%I'), TIME_TO_STR(q.CreationDate, '%I')