Entity integrity constraint - relational constraints, Database Management System

Assignment Help:

It defines that no primary key value can be null. This is as the primary key is used to recognize individual tuple in the relation. So we will not be able to recognize the records uniquely containing null values for the primary key attributes. This constraint is specified on single individual relation.

 Example: Let R be the Table

A#

B

C

Null

B1

C1

A2

B2

C2

Null

B3

C3

A4

B4

C3

A5

B1

C5

Note:

1) '#' shows the Primary key of a relation.

In the relation R above, the primary key has null values in the tuples t1 & t3. NULL value in primary key is not allowed, therefore, relation instance is an invalid instance.


Related Discussions:- Entity integrity constraint - relational constraints

Explain hierarchical model, Explain Hierarchical Model ? Hierarchical ...

Explain Hierarchical Model ? Hierarchical Model - It was established to model several kinds of hierarchical organizations which exist in the real world. It uses tree structur

Explain a data dictionary, What is a data dictionary? Data Dictionary ...

What is a data dictionary? Data Dictionary is a main source of data in a data management system.  Its major function is to carry the creation and management of data definition

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

Example of weak entity, Consider the entity type dependent related to emplo...

Consider the entity type dependent related to employee entity, which is used to keep track of the dependents of every employee. The attributes of dependents are: name, sex, birth d

Structure of the ldb, Though all the ABAP/4 Dictionary Structures that exis...

Though all the ABAP/4 Dictionary Structures that exists in the structure of the LDB, being described in Database Program, we are explaining the Dictionary Structures in the Report.

Define the term- actors and data stores, Define the term- Actors and Data...

Define the term- Actors and Data Stores Actors: An actor is the active object which drives data flow graph by producing or consuming values. Actors are attached to inputs a

Write a short note on oracle instance, Write a short note on oracle Instanc...

Write a short note on oracle Instance? Oracle Instances: An instance is the (executed) Oracle software and the memory they use. It is the instance which manipulates the data s

Identify the candidate keys, Consider the following six relation schemes an...

Consider the following six relation schemes and their corresponding sets of functional dependencies. In each case identify a. All the candidate keys b. The highest normal for

What is a checkpoint, What is a checkpoint? List the operations to be perfo...

What is a checkpoint? List the operations to be performed by the system when a checkpoint is to be taken. What does the recovery system do if there is a crash? There is large n

Entity integrity, Before defines the second type of integrity constraint, v...

Before defines the second type of integrity constraint, viz., Entity Integrity, we should be well-known with the concept of NULL. Mostly, NULL is intended as a basis for dealing

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