/    /  DBMS – Integrity Constraints

Integrity Constraints


Integrity Constraints ensure that changes made to the database by authorized users do not result in a loss of data consistency.


Integrity Constraints guard against accidental damage to the database.


The constraints on a single relation :


  • not null 
  • unique 
  • check



Not null constraint : name varchar2(10) not null


 budget numeric(10,2) not null

i.e., ‘not null’ specification prohibits the insertion of a null value for the attribute.


unique constraint : unique (A1, A2,…,An)


Here, the set of attributes A1,A2,…An forms a candidate key.

i.e., with one value of candidate key, there will be at most one tuple in the relation. 


 Check clause : The use of ‘check clause’ is to ensure that attribute values satisfy specified conditions.



Example-1 :

   create table  section

   (course_id  varchar2(9),

   section_id  varchar2(2),

   semester-id varchar2(6),

   year numeric(4)

   room_number numeric(4),

   primary key (course_id, section_id, semester_id, year),

     check (semester-id in (‘fall’, ‘winter’, ‘spring’, ‘summer’) ) ) ;


Here, We are creating a table with the following variables, and using the check clause we are checking whether the attribute values are satisfying the specified conditions.



Integrity Constraints