CBSE Class 12 Informatics Practices Triggers Notes

Download CBSE Class 12 Informatics Practices Triggers Notes in PDF format. All Revision notes for Class 12 Informatics Practices have been designed as per the latest syllabus and updated chapters given in your textbook for Informatics Practices in Standard 12. Our teachers have designed these concept notes for the benefit of Grade 12 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 12 Informatics Practices for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 12 Informatics Practices given our website

Triggers Class 12 Informatics Practices Revision Notes

Class 12 Informatics Practices students should refer to the following concepts and notes for Triggers in standard 12. These exam notes for Grade 12 Informatics Practices will be very useful for upcoming class tests and examinations and help you to score good marks

Triggers Notes Class 12 Informatics Practices

,sans-serif;">syntax :

ALTER TRIGGER trigger_name DISABLE;

For example:

ALTER TRIGGER orders_before_insert DISABLE;

Drop a Trigger

syntax :

DROP TRIGGER trigger_name;

For example:

DROP TRIGGER orders_before_insert;

Example:

create or replace trigger check_budget_EMP

after insert or update of SAL, DEPTNO on EMP

declare

cursor DEPT_CUR is select DEPTNO, BUDGET from DEPT;

DNO DEPT.DEPTNO%TYPE;

ALLSAL DEPT.BUDGET%TYPE;

DEPT_SAL number;

begin

open DEPT_CUR;

loop

fetch DEPT_CUR into DNO, ALLSAL;

exit when DEPT_CUR%NOTFOUND;

select sum(SAL) into DEPT_SAL from EMP where DEPTNO = DNO;

if DEPT_SAL > ALLSAL then

raise_application_error(-20325, 'Total of salaries in the department '|| to_char(DNO) || ' exceeds

budget');

end if;

end loop;

close DEPT_CUR;

end; /

More about triggers :

Triggers are not exclusively used for integrity maintenance. They can also be used for

• Monitoring purposes, such as the monitoring of user accesses and modifications on certain sensitive

tables.

• Logging actions, e.g., on tables: Contd..

create trigger LOG EMP

after insert or update or delete on EMP

begin

if inserting then

insert into EMP LOG values(user, ’INSERT’, sysdate); end if ;

if updating then

insert into EMP LOG values(user, ’UPDATE’, sysdate); end if ;

if deleting then

insert into EMP LOG values(user, ’DELETE’, sysdate); end if ;

end;

By using a row trigger, even the attribute values of the modified tuples can be stored in the table EMP LOG.

• automatic propagation of modifications. For example, if a manager is transferred to another department, a trigger can be defined that automatically transfers the manager’s employees to the new department.

More about Triggers

If a trigger is specified within the SQL*Plus shell, the definition must end with a point “.” in the last line. Issuing the command run causes SQL*Plus to compile this trigger definition.

A trigger definition can be loaded from a file using the command @. Note that the last line in the file must consist of a slash “/”.

A trigger definition cannot be changed, it can only be re-created using the or replace clause.

The command drop deletes a trigger.

After a trigger definition has been successfully compiled, the trigger automatically is enabled.

The command alter trigger disable is used to deactivate a trigger. All

triggers defined on a table can be (de)activated using the command

alter table enable | disable all trigger;

The data dictionary stores information about triggers in the table USER TRIGGERS. The information includes the trigger name, type, table, and the code for the PL/SQL block.

Difference b/w For and Do Loops: When No. of repetitions are known then For loop is used, and if the No. of iterations are unknown then do loops are used.

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