以倍之間的長度的平均值，並添加列查詢

Question

見下面的查詢

Select avg(datediff(,date1, date2)) as Avg_TOTALLengthofServicePerMember. 

現在我想創建另一個查詢。

select 
    id, date1, date2, datediff(date1,date2) as Memberdiff, 
    Avg_TOTALLengthofServicePerMember 

結果應該是...

ID Date1  Date2  Memberdiff  Avg_TOTAlLengthofServicePerMember 
1  1/1/2015 1/2/2015  1    10 
2  1/1/2015 1/3/2015  2    10 

Answer 1

這是我最好的結果是工程...

select M1.id, M1.date1, M1.date2, avg(datediff(day, date1, date2)) as Memberdiff , (select avg(datediff(day, date1, date2)) from m) as Avg_TOTAlLengthofServicePerMember 
FROM M1 
GROUP BY M1.id, M1.date1, M1.date2