Integrity Constraints in DBMS

Integrity Constraints

• The Set of rules which is used to maintain the quality of information are known as integrity constraints.
• Integrity constraints make sure about data intersection, update and so on.
• Integrity constraints can be understood as a guard against unintentional damage to the database.

 

Different types of Integrity Constraints

Domain Constraint

• The Definition of an applicable set of values is known as domain constraint.
• Strings, character, time, integer, currency, date etc. Are examples of the data type of domain constraints.

Example

ID	NAME	SEMESTER	AGE
100	Jai	1st	27
101	BKadam	4th	34
102	Rajeev	3rd	31
103	Asmita	6th	29
104	Mahesh	2nd	Twenty two

‘Twenty two’ is not allowed for 104 id because the attribute AGE is an integer

 

Entity Integer Constraint

• Entity Integrity Constraints states that the primary value key cannot be null because the primary value key is used to find out individual rows in relation and if the value of the primary key is null then it is not easy to identify those rows.
• There can be a null value in the table apart from the primary key field.

Example

Emp_ID	Emp_Name	Salary
11	Manish	30000
12	Vikram	20000
13	Sudhir	10000
	Rajeev	40000

Null is not allowed in Emp_ID as it is a Primary key and cannot have a NULL value.

 

Referential Integrity Constraint

1. Referential Integrity Constraint is specific between two tables.
2. A foreign key in the 1^st table refers to the primary key of the 2^nd table, in this case each value of the foreign key in the 1^st table has to be null or present in the 2^nd table.

Key Constraints

• The Entity within its entity set is identified uniquely by the key which is the entity set.
• There can be a number of keys in an entity set but only one will be the primary key out of all keys. In a relational table a primary key can have a unique as well as a null value.

Example

ID	NAME	SEMESTER	AGE
100	Naren	4	27
101	Lalit	6	28
102	Shivanshu	3	22
103	Navdeep	5	29
102	Karthik	7	25

All row ID must be unique hence 102 is not allowed.