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

Visio diagram - database, The database depicted in the Visio diagram descri...

The database depicted in the Visio diagram describes Proceeding , Article , Researcher , article PublishedIn a proceeding, article WrittenBy researchers and proceedings Edi

Explain nested relations, Explain nested relations? Nested relations ...

Explain nested relations? Nested relations The assumption of INF is a natural one in the bank examples we have considered. However, not all applications are best modelled

Assigning responsibility for operation, Assigning Responsibility for Operat...

Assigning Responsibility for Operation Many operations might have obvious target objects, but some of these operations could be used at numerous places in an algorithm, by one

Assignment, What are the typical phases of query processing

What are the typical phases of query processing

Data definition language, Data Definition Language It organises the dat...

Data Definition Language It organises the data in the form of columns and rows. But what does the data field column of table accumulate? How do you describe it using SQL? Th

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

Define the term- making common behaviour abstract, Making Common Behaviour ...

Making Common Behaviour Abstract Let us define abstraction "Abstraction means to focus on the necessary, inherent aspects of an entity and ignoring its accidental features". O

Describe the capabilities offered via mysql client apis, Describe the capab...

Describe the capabilities offered via MySQL client APIs? . • Checking for errors. . • Connecting to the MySQL server, selecting a database, disconnecting from the server

Define first normal form and second normal form, First Normal Form and seco...

First Normal Form and second normal form First Normal Form (1NF) A relation is said to be in 1NF if it having no non-atomic values and each row can give a unique combinat

Explain how the associations are implemented as classes, Explain how the as...

Explain how the associations are implemented as classes. A general approach in this case is to transform an association class into a simple class linked to two original classes

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