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

Datawarehouse, Explain four causes for failures in data warehouse projects

Explain four causes for failures in data warehouse projects

Explain the object-oriented decomposition, Explain the Object-oriented deco...

Explain the Object-oriented decomposition Object-oriented decomposition targets at identifying individual sovereign objects that encapsulate both a state and certain behavio

What is the main advantage of the object model, What is the main advantage ...

What is the main advantage of the object model? What are its different components? The object model focuses on the logical data structures. Each object model comprises of many

Backward recovery (undo), Backward Recovery (UNDO): In this system the unco...

Backward Recovery (UNDO): In this system the uncommitted changes made by a transaction to a database are undone.  Instead the system is reset to the last consistent state of databa

Failures and recovery, Failures and Recovery In practice various things...

Failures and Recovery In practice various things might occur to prevent a transaction from completing. Recovery methods are used to bring database, which does not satisfy consi

Join relation of two tuples, Consider the join of a relation R with relatio...

Consider the join of a relation R with relation S. If R has m tuples and S has n tuples, then the maximum size of join is: If R has m tuples and S has n tuples then maximum siz

Explain the natural join, Explain the Natural join Natural join is a bi...

Explain the Natural join Natural join is a binary operator which is written as (R* S) in which R and S are relations. The effect of the natural join is the set of all combinati

E - r schema with weak entity, Consider the E/R schema with weak entity set...

Consider the E/R schema with weak entity sets shown below. Come up with the SQL CREATE TABLE statements (with appropriate primary key, unique and foreign key constraints). Include

Explain the five levels of capability maturity models, Question 1 What is ...

Question 1 What is data mining? Write Data Mining applications Question 2 What is OLAP? Write the benefits of OLAP Question 3 What is Business Intelligence? Explai

What is a block and a block number, What is a block and a block number? ...

What is a block and a block number? A block is a contiguous sequence of sectors from a single track of one platter. Every request specifies the address on the disk to be refere

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