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.

Reference

Integrity Constraints