Dealing with constraints violation, Database Management System

Assignment Help:

If the deletion violates referential integrity constraint, then three alternatives are available:

Default option: - refuse the deletion. It is the job of the DBMS to describe to the user why the deletion was rejected.
Attempt to propagate (or cascade) the deletion by deleting tuples that reference the tuple that is being deleted.
Vary the value of referencing attribute that origins the violation.

Example:

Let R:

A#	B	C^
A1	B1	C1
A2	B3	C3
A3	B4	C3
A4	B1	C5

C#	D
C1	D1
C3	D2
C5	D3

Note:

1) '#' shows the Primary key of a relation.

2) '^' shows the Foreign key of a relation.

(1) Delete a tuple with C# = 'C1' in Q.

Violated constraint: - Referential Integrity constraint

Motive: - Tuples in relation A refer to tuple in Q.

Dealing: - Options available are

1) Decline the deletion.

2) DBMS may automatically delete all tuples from relation S and Q with C

# = 'C1'. This is known as cascade detection.

3) The one more option would result in putting NULL value in R where C1 exist, which is the initial tuple R in the attribute C.

Related Discussions:- Dealing with constraints violation

Query to delete constraint from alter table, A constraint named less_than_2...

A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;

RDM & ER Modelling, #questiRegional Gardens has many nurseries, including W...

#questiRegional Gardens has many nurseries, including Wagga Wagga, Bathurst, Albury, Orange, and Dubbo. Each nursery is known by its campus code, eg WW, B, A, O and D respectively.

Hangman, a method named WonGame that checks each letter in the word is matc...

a method named WonGame that checks each letter in the word is matched by its label

Name the various privileges in sql, Name the various privileges in SQL? ...

Name the various privileges in SQL? A) Delete B) Select C) Insert D) Update

Partial relation emp-get the details people with min salary, Let consider t...

Let consider the given partial relation EMP. Let us make some sub-queries for them EMPNO ENAME JOB SAL DEPTNO 7566

What are the comparison operator in sql, What are the comparison operator i...

What are the comparison operator in SQL? Comparison operator in SQL are =, LIKE and BETWEEN

Compare three clustering algorithms in weka, Compare three clustering algor...

Compare three clustering algorithms in Weka. For this comparison, you will need to use at least two different datasets. Run the algorithms on the datasets, and use the visual

Describe physical data independence, Describe Physical Data independence ? ...

Describe Physical Data independence ? Physical Data Independence - It is capacity to modify the internal schema without having to change conceptual schema. Therefore, the exter

ER Modeling, explain ER Modeling?

explain ER Modeling?

Explain the term- event, Event Occurrence of a process is called event...

Event Occurrence of a process is called event. In other words, the object can receive many input instructions. The changes which occur due to these instructions are known as e

Write Your Message!

Name

Email id

Message

Verfication Code

User Account

All Pages