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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