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

OLD HOME POLICIES, Write an sql statement to find what is the percentage of...

Write an sql statement to find what is the percentage of home policies which are from the state of Arizona out of all Home policies by Policy Value.

Explain the paths in the association network, Explain the paths in the asso...

Explain the paths in the association network We can analyze use of paths in the association network as given below: Calculate each operation Find associations whic

Objectives-database recovery and security, Objectives Define the te...

Objectives Define the terms RECOVERY and INTEGRITY; Define Recovery Techniques; Explain Error and Error detection techniques, and Define types of Authorisation.

Draw an e_r model in oracle, Draw an E_R Model for the following: An or...

Draw an E_R Model for the following: An organization uses number of items of a equipment to generates goods. Each item is at one LOCATION, of one TYPE and has a DETAILED_DISCRI

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

Transactions t1 and t2 are in a deadlock, Evaluate: a.When transactions...

Evaluate: a.When transactions T1 and T2 are in a deadlock, one of the transactions will eventually implement to completion and let the other one continue implementation. b.

Give an example of object representation, Give an example of Object Represe...

Give an example of Object Representation  For illustration, consider the implementation of a social security number within an employee object that is shown in Figure. The soci

Types of indexes, Types Of Indexes One of the words used during the fil...

Types Of Indexes One of the words used during the file organisation is the term index. In this part, let us describe this term in more detail. We find the index of keywords

Multivalued attributes, For every multivalued attribute 'A', we make a new ...

For every multivalued attribute 'A', we make a new relation R that contains an attribute corresponding to plus the primary key attribute k of the relation that shows the entity typ

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