你管理一个SQL Server 2008数据库，其中包含名为dbo.Sales的表，该表包含下面的表定义：CREATETAB

你管理一个SQL Server 2008数据库，其中包含名为dbo.Sales的表，该表包含下面的表定义：

CREATE

TABLE [dbo].[Sales]([SalesID] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY

CLUSTERED,[OrderDate] [datetime] NOT NULL,[CustomerID] [int] NOT

NULL,[SalesPersonID] [int] NULL,[CommentDate] [date] NULL);

此表包含数百万条订单。你运行下面的查询来确定销售人员何时在dbo.Sales表中提供备注：

SELECT SalesID,CustomerID,SalesPersonID,CommentDate FROM dbo.SalesWHERE CommentDate IS NOT NULL AND SalesPersonID IS NOT NULL;

你发现此查询运行很慢。检查数据之后，你发现只有1%的行有备注日期，10%的行的SalesPersonID为null。你需要创建索引来优化此查询。索引必须在优化查询的同时节省磁盘空间。应创建哪个索引（）？

A.CREATE NONCLUSTERED INDEX idx1 ON dbo.Sales (CustomerID) INCLUDE (CommentDate)WHERE SalesPersonID IS NOT NULL;

B.CREATE NONCLUSTERED INDEX idx1 ON dbo.Sales (SalesPersonID) INCLUDE (CommentDate,CustomerID);

C.CREATE NONCLUSTERED INDEX idx1 ON dbo.Sales (CustomerID) INCLUDE(CommentDate,CustomerID);

D.CREATE NONCLUSTERED INDEX idx1 ON dbo.Sales (CommentDate, SalesPersonID) INCLUDE(CustomerID) WHERE

CommentDate IS NOT NULL;