OVER Clause是个好东西，常和ROW_NUMBER()、Sum、AVG、Count、Min、Max配合使用

根据SQL官方帮助的实例：

USE AdventureWorks2012;
GO
SELECT ROW_NUMBER() OVER(PARTITION BY PostalCode ORDER BY SalesYTD DESC) AS "Row Number",
    p.LastName, s.SalesYTD, a.PostalCode
FROM Sales.SalesPerson AS s
    INNER JOIN Person.Person AS p
        ON s.BusinessEntityID = p.BusinessEntityID
    INNER JOIN Person.Address AS a
        ON a.AddressID = p.BusinessEntityID
WHERE TerritoryID IS NOT NULL
    AND SalesYTD <> 0
ORDER BY PostalCode;
GO

Row_Number() 以PARTITION BY PostalCode分隔，按照ORDER BY SalesYTD DESC排序

实际效果类似

官方其他例子：

USE AdventureWorks2012;
GO
SELECT SalesOrderID, ProductID, OrderQty
    ,SUM(OrderQty) OVER(PARTITION BY SalesOrderID) AS Total
    ,AVG(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Avg"
    ,COUNT(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Count"
    ,MIN(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Min"
    ,MAX(OrderQty) OVER(PARTITION BY SalesOrderID) AS "Max"
FROM Sales.SalesOrderDetail
WHERE SalesOrderID IN(43659,43664);
GO

　结果：

SalesOrderID ProductID   OrderQty Total       Avg         Count       Min    Max
------------ ----------- -------- ----------- ----------- ----------- ------ ------
43659        776         1        26          2           12          1      6
43659        777         3        26          2           12          1      6
43659        778         1        26          2           12          1      6
43659        771         1        26          2           12          1      6
43659        772         1        26          2           12          1      6
43659        773         2        26          2           12          1      6
43659        774         1        26          2           12          1      6
43659        714         3        26          2           12          1      6
43659        716         1        26          2           12          1      6
43659        709         6        26          2           12          1      6
43659        712         2        26          2           12          1      6
43659        711         4        26          2           12          1      6
43664        772         1        14          1           8           1      4
43664        775         4        14          1           8           1      4
43664        714         1        14          1           8           1      4
43664        716         1        14          1           8           1      4
43664        777         2        14          1           8           1      4
43664        771         3        14          1           8           1      4