Trigger on update of an attribute of a table in SQL Server? - sql

Question

I created computer audit application. When I ran my application, it shows computer accessories on browser like computerName, osVersion, lastAudit, model, totalMemory, processor, userName.
I have created a database in SQL Server 2008 with one table Computers. When a value is inserted into that table, I need to update the table value in the column. In an attempt to try this, I'm using a trigger. However, I do not fully understand how triggers work.
Can someone please show me how to accomplish this.
My table has these columns:
id, computerName, osVersion, lastAudit, model, totalMemory, processor, userName
I know that in this code something wrong or missing but I am not able to complete this. Please help me in this regard.
CREATE TRIGGER update_trigger
ON computers
AFTER UPDATE
AS
BEGIN
declare #id as int
declare #computerName as varchar(100)
declare #osVersion as varchar(100)
declare #lastAudit as datetime
declare #model as varchar(100)
declare #totalMemory float
declare #processor as varchar(100)
declare #userName as varchar(100)
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
if update(id)
BEGIN
insert into computers values(#id,#computerName,#osVersion,#lastAudit,#model,
#totalMemory,#processor,#userName,'Update')
SET NOCOUNT ON;
END
GO

Answer 1

If you want to simply update one or more columns of your existing table when new rows are being inserted (or when they are updated? Not quite clear...), try a trigger like this:
CREATE TRIGGER trigUpdateTable
ON dbo.Computers
AFTER INSERT -- or AFTER UPATE or AFTER INSERT, UPDATE
AS
BEGIN
-- do whatever you want to do on INSERT and/or UPDATE
UPDATE
dbo.Computers
SET
LastAudit = GETDATE()
FROM
dbo.Computers c
INNER JOIN
Inserted i ON c.id = i.id
One very important point to remember: SQL Server triggers are not called per row that is affected - but per statement, and if your INSERT or UPDATE statement affects multiple rows, you'll have multiple entries in the Inserted pseudo table and you need to be able to deal with that fact in your trigger