Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 15: Triggers
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To illustrate this, let’s take a look at the Sales.SalesOrderDetail and Sales.SpecialOfferProduct
tables in the AdventureWorks2008 database. The relationship looks like Figure 15-2.
Figure 15-2
So under normal DRI, you can be certain that no SalesOrderDetail item can be entered into the
SalesOrderDetail table unless there is a matching ProductID in the SpecialOfferProduct table (even
if the special offer record is “no discount”). We are, however, looking for something more than just the
norm here.
Our Inventory department has been complaining that our Customer Support people keep placing orders
for products that are marked discontinued. They would like to have such orders rejected before they get
into the system.
We can’t deal with this using a CHECK constraint, because the place where we know about the discontinued
status (the Product table) is a separate table from where we are placing the restriction (the SalesOrderDetail
table). Don’t sweat it though — you can tell the Inventory department, “No problem!”
You just need to use a trigger:
CREATE TRIGGER Sales.SalesOrderDetailNotDiscontinued
ON Sales.SalesOrderDetail
FOR INSERT, UPDATE
AS
IF EXISTS
(
SELECT ‘True’
FROM Inserted i
JOIN Production.Product p
ON i.ProductID = p.ProductID
WHERE p.DiscontinuedDate IS NOT NULL
)
BEGIN
RAISERROR(‘Order Item is discontinued. Transaction Failed.’,16,1)
ROLLBACK TRAN
END