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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.
List any two significant differences between a file processing system and a DBMS. File Processing System vs. DBMS Data Independence - Data independence is the capacity t
Describe substring comparison in SQL. For the relation Person (name, address), write a SQL query that retrieves the names of people whose name starts along with ‘A' and address co
What is deadlock? Neither of the transaction can ever proceed with its normal implementation. This situation is known as deadlock.
Strong entity set and weak entity set? Strong entity set and weak entity set: A strong entity set has a primary key. All tuples in the set are distinguishable through that key.
Most computer systems authenticate users by asking them for the user name and password. However, the user names and passwords often can be guessed by hackers. Suggest an automated,
design a generalization specialization hierarchy for a motor vehicle sales company. the company sells motorcycles, passenger cars, vens and buses.
explain the steps for reduction of er model into relational model?
What is transaction? Transaction is a unit of program implementation that accesses and possibly updated several data items.
i want to database for online assignment submission system
Column Constraints: NOT NULL, UNIQUE, CHECK, PRIMARY KEY, DEFAULT, REFERENCES, On delete Cascade : Using this key whenever a parent row is removed in a referenced
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