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

Improved availability, Improved availability: The data in a distributed sys...

Improved availability: The data in a distributed system may be replicated so that it is at more than one site. Thus, the failure of a node or a communication link does not necessar

Client server databases, Client Server Databases- The concept behind the C...

Client Server Databases- The concept behind the Client/Server systems is simultaneous, cooperative processing. It is an approach that presents a one systems view from a user's vie

Describe the candidate key functions, Describe the candidate key functions ...

Describe the candidate key functions ? Candidate Key and Alternate Key: In some instances, an entity will have more than one attribute which can serve as a primary key. Any key

Select statement-data manipulation language, SELECT Statement This stat...

SELECT Statement This statement is used for retrieving information from the databases. It can be coupled with many clauses. Let us talk about these clauses in more detail:

What is recovery management component, What is recovery management componen...

What is recovery management component? Ensuring durability is the responsibility of a software component of the base system known as the recovery management component.

Managing databases, 10A.53 Code an Oracle Database trigger to enforce the...

10A.53 Code an Oracle Database trigger to enforce the constraint that an employee can never change his or her department. 10A.54 Code an Oracle Database trigger to allow the

Define two phase commit, Define Two phase commit Two phase commit: To m...

Define Two phase commit Two phase commit: To make sure atomicity, all the sites where a transaction is being executed must agree on the final outcome of the execution. The tran

What is a sub-query, (a) What is a Sub-Query? (b) What is the differen...

(a) What is a Sub-Query? (b) What is the difference between a scalar sub-query and a tabular sub-query? (c) Write an equivalent SQL statement to get the Name of Product wh

Define the terms physical schema and logical schema., Define the terms 1) p...

Define the terms 1) physical schema 2) logical schema. Physical schema: The physical schema explains the database design at the physical level, which is the lowest level of abs

Explain how the law ensures data protection and security, Question 1: (...

Question 1: (a) Explain the legal meaning of :- (i) Computer Service Person (ii) Data holding (b) Explain how the law ensures Data protection and Security. Qu

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