SQL Server - Bài 9

Implementing
Data Integrity
Vu Tuyet Trinh

Hanoi University of Technology
1
MicrosoftMicrosoft
Data Integrity

Defining the quality of the data in the database.

Types:
Domain Integrity
(columns)
Entity Integrity (rows)
Referential
Integrity
(between tables)
User-defined
integrity
MicrosoftMicrosoft
Enforcing Data Integrity

Declarative data integrity

Defined in object definitions

Enforced automatically SQL Server by using constraints,
defaults, and rules

Procedural data integrity


Defined in script

Enforced by executing scripts, triggers and stored procedures
MicrosoftMicrosoft
Outline
√
Data Integrity

Enforcing Data Integrity

Types of Constraints

Defining Constraints

Disabling Constraints

Using Defaults and Rules

Deciding enforcement method to use
MicrosoftMicrosoft
Types of Constraints

PRIMARY KEY constraints

UNIQUE constraints

FOREIGN KEY constraints

CHECK constraints


DEFAULT constraints

Cascading referential integrity
MicrosoftMicrosoft
PRIMARY KEY Constraints

Only one PRIMARY KEY constraint per table

Unique values

Not allowed NULL values

Enforced with unique index
USE Northwind
ALTER TABLE dbo.Customers
ADD CONSTRAINT PK_Customers
PRIMARY KEY NONCLUSTERED (CustomerID)
MicrosoftMicrosoft
UNIQUE Constraints

Defined with one or more columns

Allowing one null value

Allowing multiple UNIQUE constraints on a table

Enforced with a unique Index
USE Northwind
ALTER TABLE dbo.Suppliers

ADD CONSTRAINT U_CompanyName
UNIQUE NONCLUSTERED (CompanyName)
MicrosoftMicrosoft
FOREIGN KEY Constraints

Single or multi-column referential integrity

Must reference a PRIMARY KEY or UNIQUE constraint

Must have SELECT or 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)