7
SQL OVER（）子句-何时以及为何有用？
USE AdventureWorks2008R2; 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); 我读到该条款，但我不明白为什么需要它。该功能Over做什么？怎么Partitioning By办？为什么我不能用文字查询Group By SalesOrderID？