Entity integrity constraint - relational constraints, Database Management System

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.

Posted Date: 3/6/2013 5:31:24 AM | Location : United States







Related Discussions:- Entity integrity constraint - relational constraints, Assignment Help, Ask Question on Entity integrity constraint - relational constraints, Get Answer, Expert's Help, Entity integrity constraint - relational constraints Discussions

Write discussion on Entity integrity constraint - relational constraints
Your posts are moderated
Related Questions
What is called a query -execution engine? The query implementation engine takes a query evaluation plan, implements that plan, and returns the answers to the query.

What is a view? How it is related to data independence? A view might be thought of as a virtual table, that is, a table that does not really exist in its own right but is inste

Explain the structure of well formed formulae in relational calculus. Ans: a. An atom is a formula b. If P1 is a formula, after that so are ¬P1 and (P1) c. If P1 and P2 a

Why are cursors necessary in embedded SQL? A cursor is an object used to store the output of a query for row-by-row processing through the application programs. SQL statements

What are the advantages of DBMS ? 1. Centralized Management and Control - One of the major advantages of using a database system is in which the organization could exert, thr

Problem 1. Create a PL/SQL program to insert data into student table and display the details of the student having Reg.No 1010 Writing a PL/SQL program to Insert data

Explain the main advantages of DBMS over File Oriented System ?

In how many parts events are classified Events are classified as four types in UML 1.  Signals 2.  Calls 3.  Passing of Time 4.  Change in State

Project Description: We have an encrypted HSQL Database which we want to change into csv format. HSQL DB . We have java application (jar file) which reads that database but n

A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;