s.ไม่จำเป็นที่จะต้องใช้ทุกตาราง
s.It is not neccessary to use all the tables.
 PostHistoryTypes:  Id [ number]  Name [ text] 
SELECT YEAR(p.CreationDate), SUM(CASE WHEN NOT t.Id IS NULL THEN 1 ELSE 0 END) / CAST(COUNT(p.Id) AS FLOAT) AS "ratio of id requests" FROM Posts AS p JOIN PostTags AS pt ON pt.PostId = p.Id LEFT OUTER JOIN Tags AS t ON t.Id = pt.TagId AND t.TagName = 'single-word-requests' WHERE p.PostTypeId = 1 GROUP BY YEAR(p.CreationDate)