SQL Server触发器Trigger(2)

下面表[OrderDemo]有一个字段[Num]，此字段作为排序字段，在插入时它的值为主键一样，但不能设为IDENTITY自动增长，因为它有可能被更新为其它值。

IF OBJECT_ID('[dbo].[OrderDemo]') IS NOT NULL
    DROP TABLE [dbo].[OrderDemo]
GO

CREATE TABLE [dbo].[OrderDemo]
(
    OrderDemoId INT IDENTITY(1,1) PRIMARY KEY NOT NULL,
    [Name] NVARCHAR(50) NOT NULL,
    [Num] INT NULL  
)
GO

现在我们需要写一个触发器(AFTER INSERT)，当在记录插入时，把记录自动产生的主键值写入这个字段中。

IF EXISTS (SELECT [name] FROM sysobjects WHERE [name] = 'tri_OrderDemo_Insert' AND TYPE = 'TR')
   DROP TRIGGER [dbo].[tri_OrderDemo_Insert]
GO

CREATE TRIGGER [dbo].[tri_OrderDemo_Insert] ON [dbo].[OrderDemo]
AFTER INSERT
AS
DECLARE @PK INT 
SELECT @PK = [OrderDemoId] FROM inserted
UPDATE [dbo].[OrderDemo] SET [Num] = @PK WHERE [OrderDemoId] = @PK