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

What is secondary index, What is Secondary Index While making the index...

What is Secondary Index While making the index, generally the index table is kept in the primary memory (RAM) and the main table, because of its size is keeps in the secondary

Skills required, wrie a report on whether a BSc n information systems devel...

wrie a report on whether a BSc n information systems develops the skills required by employers in Database administration

Decompose the table - 3nf or bcnf, Decompose the table with the following ...

Decompose the table with the following description and functional dependencies into a set of equivalent tables normalized to 3NF or BCNF. A long-standing international treaty am

Relational operations, Let us now talk about the relational operations: ...

Let us now talk about the relational operations: SELECT The select operation is used to select few specific record from the database based on different criteria, This is a un

What is meant by object identifiers, What is meant by object identifiers? ...

What is meant by object identifiers? Object-oriented systems use an object identifier to recognize objects. Object identifiers are unique: that is every object has a single ide

Large Project, Can you help me with the following: Drop statements for all...

Can you help me with the following: Drop statements for all objects in the lab project. Create statements for all objects of the lab project Create indexes for foreign keys Cre

What are advantages of object-oriented programming paradigm, What is the ma...

What is the major advantage of object-oriented programming paradigm? The ability to modify the explanation of an object without affecting the rest of the system is the main adv

How is concurrency identified, How is concurrency identified? Concurren...

How is concurrency identified? Concurrency in objects can be identified by the way they alter their state. Current objects can change their state independently. Aggregation imp

What you understand by client-server environment, Problem: a) Briefly d...

Problem: a) Briefly describe what you understand by Client-Server environment b) The File Server is a simple form of Client-Server. Describe the principles of the File Serve

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