Delete - referential integrity, Database Management System

Assignment Help:

During the deletion of a tuple two cases can happen:

Deletion of tuple in relation having the foreign key: In this type of case simply delete the desired tuple. For example, in ASSIGNMENT relation we can simply delete the first tuple.

Deletion of the target of a foreign key reference: For instance, an attempt to delete an employee tuple in EMPLOYEE relation whose EMPID is 101. This employee shown not only in the EMPLOYEE but also in the ASSIGNMENT relation. Can these tuple be deleted? If we delete the tuple in EMPLOYEE relation then two unequalled tuples are left in the ASSIGNMENT relation, therefore causing violation of referential integrity constraint. Therefore, the following two choices be for such deletion:

RESTRICT - The delete operation is "restricted" to only the situation where there are no such matching tuples.    For instance, we can delete the EMPLOYEE record of EMPID 103 as there is no matching tuple in ASSIGNMENT but not the record of EMPID 101.

CASCADE - The delete operation "cascades" to delete also those matching tuple. For  instance,  if  the  delete  mode  is  CASCADE  then  deleting  employee  having

EMPID as 101 from EMPLOYEE relation will also make deletion of 2 more tuples from ASSIGNMENT relation.


Related Discussions:- Delete - referential integrity

Assignment, am looking for assignment helper for dbms

am looking for assignment helper for dbms

Object query language and odmg schema , (a)    Provide the description of t...

(a)    Provide the description of the following ODMG schema in the Object Definition Language (ODL). (b)   Based on the above object database, write the following queries i

Write the syntax of creating an index, Write the syntax of creating an INDE...

Write the syntax of creating an INDEX ? Syntax of Creating an Index: CREATE [BITMAP] [UNIQUE] INDEX ON ( [, ] . . .);

What is conceptual schema, What is Conceptual Schema? Conceptual Schema...

What is Conceptual Schema? Conceptual Schema - Conceptual schema elaborates the structure of the overall database for a community of users. It hides the details of physical sto

Which product produces the relation that has attributes, Which product prod...

Which product produces the relation that has attributes of R1 and R2 ? Cartesian product produce the relation which has attributes of R1 and R2

Define tables students and teachers as sub tables of people, Write a query ...

Write a query to define tables students and teachers as sub tables of people? Create table students of student under people Create table teachers of teacher under people

Illustrate the state model for the atm class, Illustrate the State model fo...

Illustrate the State model for the ATM class let us take state model for the ATM class given below in Figure showing state model of the ATM class and the pseudo code derived fr

Modifyand removing a sequence-sequences, Modify a sequence: ALTER SEQU...

Modify a sequence: ALTER SEQUENCE SEQSS INCREMENT 2 MAXVALUE 3000;   Removing a sequence: DROP SEQUENCE SEQSS;

Sequential file organisation, Sequential File Organisation The most nec...

Sequential File Organisation The most necessary way to organise the collection of records in a file is to use sequential Organisation. Records of the file are stored in series

What is a database, What is a Database? To know what database is, we ha...

What is a Database? To know what database is, we have to start from data, which is the basic building block of any DBMS. Data: Facts, figures, statistics etc. having no pa

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