用VS2005时发现一个问题，生成数据集时，VS会帮你自动优化语句，一般都不怀疑微软的水平，不过这次优化之后实在是看不懂了，怀疑优化错了，于是在查询分析器里试了一下，结果倒是对的，可是执行计划里却显示优化后的效率低一些，奇怪了
下面代码里前一行是我写的，后一行是VS优化出来的(使用了SQL Server自带的Northwind数据库)：
declare @shipName varchar declare @ShipCity varchar set @shipName = '' set @ShipCity = '' SELECT dbo.Orders.OrderID, dbo.Orders.OrderDate, dbo.Employees.FirstName, dbo.Customers.CompanyName FROM dbo.Customers INNER JOIN dbo.Orders ON dbo.Customers.CustomerID = dbo.Orders.CustomerID INNER JOIN dbo.Employees ON dbo.Orders.EmployeeID = dbo.Employees.EmployeeID WHERE (shipName = @shipName OR @shipName = '' ) AND (shipcity = @ShipCity OR @ShipCity = '' ) AND ShipVia = 2 SELECT Orders.OrderID, Orders.OrderDate, Employees.FirstName, Customers.CompanyName FROM Customers INNER JOIN Orders ON Customers.CustomerID = Orders.CustomerID INNER JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID WHERE (Orders.ShipName = @shipName OR @shipName = '' ) AND (Orders.ShipCity = @ShipCity ) AND (Orders.ShipVia = 2 ) OR (Orders.ShipName = @shipName OR @shipName = '' ) AND (Orders.ShipVia = 2 ) AND ( @ShipCity = '' )执行计划显示查询成本分别是：49.49%和50.51%
另外就是看不懂优化后的where后面是什么意思，郁闷ing~~~~~记下这笔，有时间研究下
