Database Management
Systems
( B.Tech. II Year II Sem R-18 )
CSE
Integrity Constraints in DBMS
⚫ Relational constraints are the restrictions imposed
on the database contents and operations.
⚫ They ensure the correctness of data in the database
In DBMS, there are following 5 different types of
relational constraints-
1. Domain constraint
2. Tuple Uniqueness constraint
3. Key constraint
4. Entity Integrity constraint
5. Referential Integrity constraint
Domain Constraint
•Domain constraint defines the domain or set of values for an attribute.
•Composite or multivalued attributes are not allowed
•It specifies that the value taken by the attribute must be the atomic value from its
domain.
Example-
Consider the following Student table-
Here, value ‘A’ is not allowed since only integer values can be taken by the age
attribute.
STU_ID Name Age
5001 Akshay 20
5002 Abhishek 21
5003 Shashank 20
5004 Rahul Abc
Tuple Uniqueness Constraint
Tuple Uniqueness constraint specifies that all the tuples must be necessarily unique
in any relation.
Example-01:
Consider the following Student table-
STU_ID Name Age
S001 Akshay 20
S002 Abhishek 21
S003 Shashank 20
S004 Rahul 20
This relation satisfies the tuple uniqueness constraint since here all the tuples are
unique
Tuple Uniqueness Constraint
Example-02:
Consider the following Student table-
This relation does not satisfy the tuple uniqueness constraint since here all
the tuples are not unique.
STU_ID Name Age
S001 Akshay 20
S001 Akshay 20
S003 Shashank 20
S004 Rahul 20
Key Constraint
Key constraint specifies that in any relation-
• All the values of primary key must be unique.
• The value of primary key must not be null.
Example-01:
Consider the following Student table-
STU_ID Name Age
S001 Akshay 20
S001 Abhishek 21
S003 Shashank 20
S004 Rahul 20
This relation does not satisfy the key constraint as here all the values of
primary key are not unique.
Entity integrity constraint
Entity integrity constraint specifies that no attribute of primary key must contain a
null value in any relation.
This is because the presence of null value in the primary key violates the
uniqueness property.
Example-01:
Consider the following Student table-
STU_ID Name Age
S001 Akshay 20
S002 Abhishek 21
S003 Shashank 20
Rahul 20
This relation does not satisfy the entity integrity constraint as here the
primary key contains a NULL value
Referential Integrity Constraint
This constraint is enforced when a foreign key references the primary key of a relation.
It specifies that all the values taken by the foreign key must either be available in the
relation of the primary key or be null.
The following two important results emerges out due to referential integrity constraint-
• We can not insert a record into a referencing relation if the corresponding record does
not exist in the referenced relation.
• We can not delete or update a record of the referenced relation if the corresponding
record exists in the referencing relation
Example-
Consider the following two relations- ‘Student’ and ‘Department’.
Here, relation ‘Student’ references the relation ‘Department’.
Referential Integrity Constraint
•Foreign key references the primary key of the table.
•Foreign key can take only those values which are present in the primary key of
the referenced relation.
•Foreign key may have a name other than that of a primary key.
•Foreign key can take the NULL value.
•There is no restriction on a foreign key to be unique.
•In fact, foreign key is not unique most of the time.
•Referenced relation may also be called as the master table or primary table.
•Referencing relation may also be called as the foreign table.
Referential Integrity Constraint
STU_ID Name Dept_no Dept_no Dept_name
S001 Akshay D10 D10 ASET
S002 Abhishek D10 D11 ALS
S003 Shashank D11 D12 ASFL
S004 Rahul D14 D13 ASHS
Student Department
Here,
•The relation ‘Student’ does not satisfy the referential integrity constraint.
•This is because in relation ‘Department’, no value of primary key specifies department no. 14.
•Thus, referential integrity constraint is violated.
