Sql server 从同一ID号获取DATEDIFF结果的平均值

这是我目前的桌子

员工将有多个订单日期和发货日期。我想得到的是每个员工的差异总和的平均值

一直在为如何实现这一目标而挣扎

这就是我到目前为止所做的

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

如果在结果集中需要的不仅仅是

EmployeeId

，请按如下方式加入：

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

如果在结果集中需要的不仅仅是

EmployeeId

，请按如下方式加入：

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

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谢谢你，米奇！我正在编辑这篇文章，然后你顺道来了。谢谢你，米奇！我正在编辑文章，然后你顺道过来。这将排除所有空行，对吗？谢谢你的帮助！这将排除所有空行，对吗？谢谢你的帮助！

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