从DATEDIFF获得平均值来自相同ID号码的结果

Question

这是我目前的表格。

员工将有多个订单日期，发货日期。我想要得到的是每位员工差异总和的平均值。

一直在努力如何实现这一目标。

这是我迄今为止所做的。

USE Northwind 

SELECT 
    e.EmployeeID, 
    e.LastName, 
    o.OrderDate, 
    o.ShippedDate, 
    DATEDIFF(DAY, o.OrderDate, o.ShippedDate) as Diff 
FROM 
    Employees as e 
    JOIN Orders as o ON e.EmployeeID = o.EmployeeID 

Answer 1

SELECT 
    e.EmployeeID, 
    AVG(CAST(DATEDIFF(DAY, o.OrderDate, o.ShippedDate) as float)) as AvgDiff 
FROM 
    Employees as e 
    JOIN Orders as o ON e.EmployeeID = o.EmployeeID 
Group By e.EmployeeID 

如果你想在结果集中比EmployeeId多，加入背像这样：

select 
    e.EmployeeId 
    e.LastName, 
    a.AvgDiff 
From 
    Employees as e 
Join  (SELECT 
       e.EmployeeID, 
       AVG(CAST(DATEDIFF(DAY, o.OrderDate, o.ShippedDate) as float)) as AvgDiff 
      FROM 
       Employees as e 
       JOIN Orders as o ON e.EmployeeID = o.EmployeeID 
      Group By e.EmployeeID) a ON a.EmployeeId = e.EmployeeId 

Answer 2

SELECT 
    e.EmployeeID, 
    e.LastName, 
    AVG(1.0 * DATEDIFF(DAY, o.OrderDate, o.ShippedDate)) as AVGDiff 
FROM 
    Employees as e 
    JOIN Orders as o ON e.EmployeeID = o.EmployeeID 
Group by e.EmployeeID, e.LastName 
Order by e.EmployeeID, e.LastName