1. Module 4: Implementing Data Integrity

2. Overview Introducing Data Integrity Defining Constraints
Understanding Constraint Types
Disabling Constraints
Using Defaults and Rules
Deciding Which Enforcement Method to Use

3. Lesson: Introducing Data Integrity
Types of Data Integrity
How Data Integrity Is Enforced

4. Types of Data Integrity
Domain Integrity (columns)
Entity Integrity (rows)
Referential Integrity (between tables or columns of the same table)

5. How Data Integrity is Enforced
Declarative Data Integrity
Criteria defined in object definitions
SQL Server enforces automatically
Implement by using constraints, defaults, and rules
Procedural Data Integrity
Criteria defined in scripts
Criteria enforced by scripts
Implement by using triggers and stored procedures

6. Lesson: Defining Constraints
Guidelines for Determining Which Type of Constraint to Use
Constraint Creation
Considerations for Using Constraints

7. Guidelines for Determining Which Type of Constraint to Use
Type of integrity
Constraint type
Domain
DEFAULT
CHECK
FOREIGN KEY
Entity
PRIMARY KEY
UNIQUE
Referential

8. Constraint Creation Use CREATE TABLE or ALTER TABLE
Can Add Constraints to a Table with Existing Data
Can Place Constraints on Single or Multiple Columns
Column-Level Constraint
Can only reference a single column
Specify as part of the column definition
Table-Level Constraint
Can reference one or more columns
Specify as part of the table definition (after all column definitions)

9. Considerations for Using Constraints
Can Be Changed Without Re-creating a Table
Require Error-Checking in Applications and Transactions
Verify Existing Data

10. Lesson: Understanding Constraint Types
DEFAULT Constraints
CHECK Constraints
PRIMARY KEY Constraints
UNIQUE Constraints
FOREIGN KEY Constraints
Cascading Referential Integrity

11. DEFAULT Constraints Apply Only to INSERT Statements
Only One DEFAULT Constraint Per Column
Cannot Be Used with IDENTITY Property or rowversion Data Type
Allow Some System-Supplied Values
USE Northwind ALTER TABLE dbo.Customers ADD CONSTRAINT DF_contactname DEFAULT 'UNKNOWN' FOR ContactName

12. CHECK Constraints Are Invoked by INSERT and UPDATE Statements
Can Reference Other Columns in the Same Table
Cannot:
Be used with the rowversion data type
Contain subqueries
USE Northwind ALTER TABLE dbo.Employees ADD CONSTRAINT CK_birthdate CHECK (BirthDate > ' ' AND BirthDate < getdate())

13. PRIMARY KEY Constraints
Only One PRIMARY KEY Constraint Per Table
Values Must Be Unique
Null Values Are Not Allowed
Creates a Unique Index on Specified Columns
USE Northwind
ALTER TABLE dbo.Customers
ADD
CONSTRAINT PK_Customers
PRIMARY KEY NONCLUSTERED (CustomerID)

14. UNIQUE Constraints Allow One Null Value
Allow Multiple UNIQUE Constraints on a Table
Defined with One or More Columns
Enforced with a Unique Index
USE Northwind
ALTER TABLE dbo.Suppliers
ADD
CONSTRAINT U_CompanyName
UNIQUE NONCLUSTERED (CompanyName)

15. FOREIGN KEY Constraints
Must Reference a PRIMARY KEY or UNIQUE Constraint
Provide Single or Multicolumn Referential Integrity
Do Not Automatically Create Indexes
Requires Users to Have REFERENCES Permissions on Referenced Tables
Use Only REFERENCES Clause Within Same Table
USE Northwind
ALTER TABLE dbo.Orders
ADD CONSTRAINT FK_Orders_Customers
FOREIGN KEY (CustomerID)
REFERENCES dbo.Customers(CustomerID)

16. Cascading Referential Integrity
NO ACTION
CASCADE
Customers
Customers
CustomerID (PK)
CustomerID (PK) 1 1
INSERT new CustomerID
UPDATE CustomerID
CASCADE
Orders 2
CustomerID (FK)
Orders
UPDATE old CustomerID to new CustomerID
CustomerID (FK)
Customers
CustomerID (PK) 3
DELETE old CustomerID

17. Lesson: Disabling Constraints
Guidelines for Disabling Constraint Checking on Existing Data
Guidelines for Disabling Constraint Checking When Loading New Data

18. Guidelines for Disabling Constraint Checking on Existing Data
Applies to CHECK and FOREIGN KEY Constraints
Use WITH NOCHECK Option When Adding a New Constraint
Existing Data Will Be Checked Only During Future Updates of the Constraint Column
Can Change Existing Data Before Adding Constraints
USE Northwind
ALTER TABLE dbo.Employees
WITH NOCHECK
ADD CONSTRAINT FK_Employees_Employees
FOREIGN KEY (ReportsTo)
REFERENCES dbo.Employees(EmployeeID)

19. Guidelines for Disabling Constraint Checking When Loading New Data
Applies to CHECK and FOREIGN KEY Constraints
Use When:
Data conforms to constraints
You load new data that does not conform to constraints
USE Northwind
ALTER TABLE dbo.Employees
NOCHECK
CONSTRAINT FK_Employees_Employees

20. Lesson: Using Defaults and Rules

21. Defaults Considerations:
Defined once, can be bound to one or more columns or user-defined data types
Rules on the column validates the value of a default
Check constraints on the column validates the value of a default.
CREATE DEFAULT phone_no_default AS '(000) ' GO EXEC sp_bindefault phone_no_default, 'Customers.Phone'

22. Rules Considerations:
Defined once, can be bound to one or more columns or user-defined data types
Can contain any expression valid in a WHERE clause
A column or user-defined data type can have only one rule that is bound to it.
CREATE RULE regioncode_rule IN ('IA', 'IL', 'KS', 'MO') GO EXEC sp_bindrule regioncode_rule, 'Customers.Region'

23. Lesson: Deciding Which Enforcement Method to Use
Functionality and Performance Considerations
Comparison Matrix
Best Practices

24. Functionality and Performance Considerations
Declarative Integrity
Use for fundamental integrity logic, such as:
When enforcing valid values
Maintaining the relationships between tables
Triggers Or Stored Procedures
Use to maintain complex redundant data that is not part of a primary or foreign key relationship

25. Data integrity components Before or after modification
Comparison Matrix
Data integrity components
Functionality
Performance costs
Before or after modification
Constraints
Medium
Low
Before
Defaults and rules
Triggers
High
Medium-High
After
Data types, Null/Not Null

26. Best Practices
Use Constraints Instead of Triggers Because They Incur Less Overhead ü ü
Use Constraints Because They Are ANSI-Compliant
Use Cascading Referential Integrity Instead of Triggers ü

27. Lab A: Implementing Data Integrity
Exercise 1: Defining DEFAULT Constraints
Exercise 2: Defining CHECK Constraints
Exercise 3: Defining PRIMARY KEY Constraints
Exercise 4: Defining FOREIGN KEY Constraints
Optional Exercise: Creating Defaults and Rules