sql server2008 联机丛书疑问

今天看到联机丛书的instead of 触发器相关章节，对其中的示例有点疑问，测试了下果然是有出入，求解释：
测试如下：

select @@version

Microsoft SQL Server 2008 R2 (RTM) - 10.50.1600.1 (X64)
Apr 2 2010 15:48:46
Copyright (c) Microsoft Corporation
Developer Edition (64-bit) on Windows NT 6.1 <X64> (Build 7601: Service Pack 1) (Hypervisor)

--测试表建立

CREATE TABLE BaseTable

  (PrimaryKey     int PRIMARY KEY IDENTITY(1,1),

   Color          nvarchar(10) NOT NULL,

   Material       nvarchar(10) NOT NULL,

   ComputedCol AS (Color + Material)

  )

GO



--Create a view that contains all columns from the base table.

CREATE VIEW InsteadView

AS SELECT PrimaryKey, Color, Material, ComputedCol

FROM BaseTable

GO



--Create an INSTEAD OF INSERT trigger on the view.

CREATE TRIGGER InsteadTrigger on InsteadView

INSTEAD OF INSERT

AS

BEGIN

  --Build an INSERT statement ignoring inserted.PrimaryKey and 

  --inserted.ComputedCol.

  INSERT INTO BaseTable

       SELECT Color, Material

       FROM inserted

END

GO

插入数据测试

--直接引用 BaseTable 的 INSERT 语句无法为 PrimaryKey 列和 ComputedCol 列提供值。例如：

--A correct INSERT statement that skips the PrimaryKey and ComputedCol columns.

INSERT INTO BaseTable (Color, Material)

       VALUES (N'Red', N'Cloth')



--View the results of the INSERT statement.

SELECT PrimaryKey, Color, Material, ComputedCol

FROM BaseTable



PrimaryKey	Color	Material	ComputedCol

1	Red	Cloth	RedCloth



--下面语句返回错误，无法为计算列提供值，报错

--An incorrect statement that tries to supply a value for the 

--PrimaryKey and ComputedCol columns.

INSERT INTO BaseTable(Color, Material,ComputedCol)

       VALUES ( N'Green', N'Wood', N'GreenWood')



>[Error] Script lines: 40-42 ------------------------

 不能修改列 "ComputedCol"，因为它是计算列，或者是 UNION 运算符的结果。

 Msg: 271, Level: 16, State: 1, Procedure: , Line: 1 

官方文档里提到下面的测试不对：

但是，引用 InsteadView 的 INSERT 语句必须为 PrimaryKey 列和 ComputedCol 列提供值：

--A correct INSERT statement supplying dummy values for the 

--PrimaryKey and ComputedCol columns.

INSERT INTO InsteadView (PrimaryKey, Color, Material, ComputedCol)

       VALUES (999, N'Blue', N'Plastic', N'XXXXXX')

--View the results of the INSERT statement.

SELECT PrimaryKey, Color, Material, ComputedCol

FROM InsteadView

 

传递到 InsteadTrigger 的所插入表是由不可为空值的 PrimaryKey 列和 ComputedCol 列生成的，因此引用该视图的 INSERT 语句必须为那些列提供值。值 999 和 N'XXXXXX' 将传递到 InsteadTrigger，但是触发器中的 INSERT 语句未选择 inserted.PrimaryKey 或 inserted.ComputedCol；因此，将忽略这两个值。实际插入到 BaseTable 的行在 PrimaryKey 中的值为 2，在 ComputedCol 中的值为 N'BluePlastic'。


但是实际结果是测试通过的，无需指定 PrimaryKey 列和 ComputedCol 列，如下：

--下面没有提供值，报错

INSERT INTO InsteadView (Color, Material)

       VALUES (N'Yellow', N'Video')



SELECT PrimaryKey, Color, Material, ComputedCol

FROM InsteadView

PrimaryKey Color Material ComputedCol
1 Red Cloth RedCloth
2 Blue Plastic BluePlastic
3 Yellow Video YellowVideo