Why if I create a trigger instead of update in SQL Server 2005, my table doesn't update?

Question

First I create a table with this script :

 CREATE TABLE [dbo].[Employee_Demo] (
    [Emp_ID] [bigint] IDENTITY (1, 1) NOT NULL ,
[Emp_Name] [varchar] (55) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
[Emp_Sal] [decimal](10, 2) NULL 
    ) ON [PRIMARY]

and then I create another table

CREATE TABLE [dbo].[Employee_Demo_Audit] (
 [Emp_ID] [int] NULL ,
 [Emp_Name] [varchar] (55) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
 [Emp_Sal] [decimal](10, 2) NULL ,
 [Audit_Action] [varchar] (100) COLLATE SQL_Latin1_General_CP1_CI_AS NULL ,
 [Audit_Timestamp] [datetime] NULL 
) ON [PRIMARY]

after that I create an INSTEAD OF UPDATE trigger on table employee_demo :

CREATE TRIGGER trgInsteadOfUpdate ON dbo.Employee_Demo
INSTEAD OF Update
AS
declare @emp_id int, @emp_name varchar(55), @emp_sal decimal(10,2), @audit_action varchar(100);
select @emp_id=i.Emp_ID from inserted i;
select @emp_name=i.Emp_Name from inserted i;
select @emp_sal=i.Emp_Sal from inserted i;  
IF UPDATE (Emp_sal)
begin
BEGIN
BEGIN TRAN
    if(@emp_sal>=1000)
    begin
    RAISERROR('Cannot Insert where salary fewer then 1000',16,1); ROLLBACK; end
    else begin
    insert into Employee_Demo_Audit(Emp_ID,Emp_Name,Emp_Sal,Audit_Action,Audit_Timestamp) values(@emp_id,@emp_name,@emp_sal,@audit_action,getdate());
    COMMIT;
    PRINT 'Record Updated -- Instead Of Update Trigger.'; END; end
end

I don't know why if I update table employee_demo with this script :

UPDATE employee_demo 
SET emp_name = 'ZHEE' 
WHERE emp_id = 1

the name of emp_id = 1 is doesn't change...

Why ????

Answer 1

这可能与以下事实有关：您在源表中使用bigint作为id，而在审计表中仅使用常规int？

Answer 2

The instead of trigger replaces the default behavior. Your trigger appears to perform an update only if the Emp_sal column is being changed. If that column is not being updated, no update statement is executed.