1. Module 6: Implementing Data Integrity by Using Triggers and XML Schemas

2. Overview
Implementing Triggers
Implementing XML Schemas

3. Lesson 1: Implementing Triggers
What Are Triggers?
How an INSERT Trigger Works
How a DELETE Trigger Works
How an UPDATE Trigger Works
How an INSTEAD OF Trigger Works
How Nested Triggers Work
Considerations for Recursive Triggers
Practice: Creating Triggers

4. What Are Triggers?
Special stored procedures that execute when INSERT, UPDATE, or DELETE statements modify a table
Two categories:
AFTER triggers execute after an INSERT, UPDATE, or DELETE statement
INSTEAD OF triggers execute instead of an INSERT, UPDATE, or DELETE statement
Trigger and the initiating statement are part of a single transaction

5. How an INSERT Trigger Works1
INSERT statement executed 2
INSERT statement logged 3
AFTER INSERT trigger statements executed
CREATE TRIGGER [insrtWorkOrder] ON [Production].[WorkOrder] AFTER INSERT AS BEGIN SET NOCOUNT ON; INSERT INTO [Production].[TransactionHistory]( [ProductID],[ReferenceOrderID],[TransactionType] ,[TransactionDate],[Quantity],[ActualCost]) SELECT inserted.[ProductID],inserted.[WorkOrderID] ,'W',GETDATE(),inserted.[OrderQty],0 FROM inserted; End

6. How a DELETE Trigger Works
DELETE statement executed 1 2
DELETE statement logged 3
AFTER DELETE trigger statements executed
CREATE TRIGGER [delCategory] ON [Categories] AFTER DELETE AS BEGIN UPDATE P SET [Discontinued] = 1 FROM [Products] P INNER JOIN deleted as d ON P.[CategoryID] = d.[CategoryID] END;

7. How an UPDATE Trigger Works1
UPDATE statement executed 2
UPDATE statement logged 3
AFTER UPDATE trigger statements executed
CREATE TRIGGER [updtProductReview] ON [Production].[ProductReview] AFTER UPDATE NOT FOR REPLICATION AS BEGIN UPDATE [Production].[ProductReview] SET [Production].[ProductReview].[ModifiedDate] = GETDATE() FROM inserted WHERE inserted.[ProductReviewID] = [Production].[ProductReview].[ProductReviewID]; END;

8. How an INSTEAD OF Trigger Works1
UPDATE, INSERT, or DELETE statement executed 2
Executed statement does not occur 3
INSTEAD OF trigger statements executed
CREATE TRIGGER [delEmployee] ON [HumanResources].[Employee] INSTEAD OF DELETE NOT FOR REPLICATION AS BEGIN SET NOCOUNT ON; int; = COUNT(*) FROM deleted; > BEGIN … END; END;

9. How Nested Triggers Work
INSERT, UPDATE, or DELETE statement 1 3
…and so on… 2
Trigger executes INSERT, UPDATE, or DELETE on another table…

10. Considerations for Recursive Triggers
Disabled by default. To enable:
Considerations:
Can exceed the 32-level nesting limit without careful design and thorough testing
Can be difficult to control the order of table updates
Can be replaced with nonrecursive logic
ALTER DATABASE AdventureWorks SET RECURSIVE_TRIGGERS ON

11. Practice: Creating Triggers
In this practice, you will:
Drop existing triggers
Create an UPDATE trigger
Create an INSTEAD OF trigger

12. Lesson 2: Implementing XML Schemas
What Are XML Schemas?
What Is an XML Schema Collection?
What Is Typed XML?
Practice: Using Typed XML

13. What Are XML Schemas?
Defines the elements and attributes that are valid in an XML document
Uses the XML Schema syntax defined by the W3C

14. What Is an XML Schema Collection?
Named collection of one or more XML schemas
Associated with columns or variables of xml data type to provide typed XML capability
Created by using CREATE XML SCHEMA COLLECTION statement

15. What Is Typed XML?
Columns or variables of the xml data type that are associated with an XML schema collection
SQL Server validates the contained XML against XML schemas in the associated XML schema collection

16. Practice: Using Typed XML
In this practice, you will:
Create an XML schema collection
Create a typed XML column
Insert valid and invalid data into a typed XML column

17. Lab: Implementing Data Integrity by Using Triggers and XML Schemas
Exercise 1: Creating Triggers
Exercise 2: Implementing XML Schemas