SQL SERVER 2012
Lecturer: Abdiaziz Ali Hassan
(M.Sc. IS, India)
E-mail: azuzsom@gmail.com
1
CHAPTER 5
DEFINING TABLES, CONT..
CONSTRAINTS
OBJECTIVES
After completing this lecture, you should be able to
answer the following questions:
 What are the different types of SQL commands
 What are constraints and how to create constraints in
SQL Server 2012
3
SQL COMMANDS

The standard SQL commands to interact with
relational databases can be classified into
groups based on their nature; and they are:
 DDL
 DML
 DCL
 DQL
SQL COMMANDS CONT..
DDL -Data Definition Language
 CREATE
 ALTER
 DROP
DML -Data Manipulation Language
 INSERT
 UPDATE
 DELETE
SQL COMMANDS CONT..
DCL -Data Control Language
 GRANT
 REVOKE
DQL -Data Query Language
 SELECT
SQL CONSTRAINTS
Constraints are the rules enforced on data
columns in a table.
 These are used to limit the type of data that
can go into a table.
 This ensures the accuracy and reliability of the
data in the database.
 In SQL, we have the following constraints:

SQL CONSTRAINTS CONT..
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NOT NULL - Indicates that a column cannot store NULL value
UNIQUE - Ensures that each row for a column must have a
unique value
PRIMARY KEY - A combination of a NOT NULL and UNIQUE.
Ensures that a column (or combination of two or more
columns) have a unique identity which helps to find a
particular record in a table more easily and quickly
FOREIGN KEY - Ensure the referential integrity of the data in
one table to match values in another table
CHECK - Ensures that the value in a column meets a specific
condition
DEFAULT - Specifies a default value when specified none for
this column
NOT NULL CONSTRAINT
Example:
UNIQUE CONSTRAINT
Example:
PRIMARY KEY
A primary key is a field in a table which uniquely
identifies each row/record in a database table.
 Primary keys must contain unique values.
 A primary key column cannot have NULL values.
 A table can have only one primary key, which may
consist of single or multiple fields.
 When multiple fields are used as a primary key,
they are called a composite key.

PRIMARY KEY
Create Primary Key Example:
SETTING A FOREIGN KEY
Primary keys uniquely identify a single row of a
table
 Foreign keys link/relate a row of data from a
second table to the primary key of the first
table

TWO RELATED TABLES
CREATING THE PRIMARY KEY
CREATING THE FOREIGN KEY
DEFAULT CONSTRAINT
Example:
ANOTHER EXAMPLE
CHECK CONSTRAINT
ANOTHER EXAMPLE
IDENTITY
MORE THAN ONE CONSTRAINT
QUESTIONS AND DISCUSSION
Thank You!!!