Key constraint - relational constraints, Database Management System

Assignment Help:

This constraint shows that the key attribute value in each tuple must be unique, i.e., no two tuples have the similar value for the key attribute. This is because the value of the primary key is used to recognize the tuples in the relation.

 

Example: If A is the key attribute in the following relation R than A1, A2 and A3 must be unique.

 

A

 

B

 

A1

 

B1

 

A3

 

B2

 

A2

 

B2

 

Example: In relation PERSON, PERSON_ID is primary key so PERSON_ID cannot be given as the similar for two persons.

Integrity Constraint

There are two kinds of integrity constraints:

  • Entity Integrity Constraint
  • Referential Integrity Constraint

Related Discussions:- Key constraint - relational constraints

What is trigger, What is trigger Triggers are statements that are imple...

What is trigger Triggers are statements that are implemented automatically by the system as the side effect of a change to the database.

What is relational calculus, What is Relational calculus? Relational c...

What is Relational calculus? Relational calculus is a Non- Procedural language.

Explain cnt in the respects of qbe, Explain CNT in the respects of QBE ? ...

Explain CNT in the respects of QBE ? CNT: It is one of the aggregation commands given in QBE. It is used to identify number of tuples

What is recovery?, What Is Recovery?  During the life of a transaction, ...

What Is Recovery?  During the life of a transaction, i.e., a after the start of a transaction but before the transaction commits, various changes may be made in a database state

Define query language, Define query language?   A query is a statement ...

Define query language?   A query is a statement requesting the retrieval of information. The portion of DML that includes information retrieval is known as a query language.

What are partial and natural key, What are partial, alternate,, artificial,...

What are partial, alternate,, artificial, compound and natural key? Partial Key: It is a set of attributes that can uniquely recognize weak entities and that are related to s

ER diegrams, How to draw an ER diagram to a finance companz

How to draw an ER diagram to a finance companz

What is object containment, What is object containment? References amon...

What is object containment? References among objects can be used to model dissimilar real-world concepts.

Create table, What are the advantages of creating a table from existing tab...

What are the advantages of creating a table from existing table?

For known, What are the function of DBA?

What are the function of DBA?

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd