This document summarizes a seminar presentation on database triggers. It defines a database trigger as procedural code that is automatically executed in response to certain events on a table or view. It discusses the types of events that can fire a trigger, including DML, DDL, system, and user events. It also outlines the need for triggers to enforce business rules, audit changes, and enhance performance. The document provides details on the major features of triggers, including the different types of triggers based on timing (before and after), scope (row and statement), and triggering event (DML, DDL, system, user). It concludes with an example of the syntax for creating a database trigger.

1. SHREE GANESH
SEMINAR ON:-
DATABASE TRIGGERS
SUBMMITED TO:-
PRIYANKA Ma’m
SUBMMITED BY
Kuldeep Kumar
Mca 3rd sem
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2. Contents-
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3. INTRODUCTION
A database trigger is
procedural code that is
automatically executed in
response to certain events
on a particular table or view
in a database.
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4. The events that fire a trigger
Event 1
• DML statements
Event 2
• DDL statements
Event 3
• System events
Event 4
• User events
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6. The need and the usage
Audit changes
Enforce business rules
Execute business rules.
Enhance performance
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7. Major Features
triggers do not accept parameters
or arguments .
triggers cannot perform commit or
rollback operations .
triggers are normally slow
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8. Type of trigger
Row
Triggers
and
Statement
Trigger
BEFORE
and
AFTER
Triggers
System
Events
and User
Events
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9. Row Triggers and Statement Trigger
Row
Triggers
• A row trigger is fired
each time the table
is affected by the
triggering statement.
Statement
Triggers
• A statement trigger is
fired once on behalf
of the triggering
statement.
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10. BEFORE and AFTER Triggers
Before
AFTER
BEFORE triggers run the trigger
action before the triggering
statement is run.
situations:
To eliminate unnecessary
processing
To derive specific column values.
• AFTER triggers run the trigger
action after the triggering statement
is run.
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11. Triggers on System Events and User
events
System
Events
User
Events
Database
startup and
shutdown
User logon
and logoff
Data Guard
role
transitions
DDL
statements
Server error
message
events
DML
statements
Exp. DBMS_AQ Package database level
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12. Parts of a Trigger
A
triggering
event or
statement
A trigger
restriction
A trigger
action
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14. THE TRIGGERING EVENT OR STATMENT
A CREATE, ALTER, or DROP statement
on any schema object
An INSERT, UPDATE, or DELETE
statement on a specific table
A database startup or instance
shutdown
A specific error message or any error
message
A user logon or logoff
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15. Trigger
Restriction
Return true and false
Exmp :new.parts_on_hand <
new.reorder_point
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16. Trigger Action
Depends of true and false
of trigger restriction.
A trigger action is the procedure (PL/SQL block, Java
program, or C callout) that contains the SQL
statements and code to be run when the following
events occur.
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17. Trigger Mode
Enabled
• An enabled trigger runs its trigger action
if a triggering statement is issued and the
trigger restriction (if any) evaluates to
true
Disabled
• A disabled trigger does not run its trigger
action, even if a triggering statement is
issued and the trigger restriction (if any)
would evaluate to false.
ALTER TRIGGER <Trigger Name> DISABLE|ENABLE
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18. Creating a Database Trigger
Name of the trigger
Table to be associated with
When trigger is to be fired - before or
after
Command that invokes the trigger UPDATE, DELETE, or INSERT
Whether row-level trigger or not
Condition to filter rows.
PL/SQL block that is to be executed
when trigger is fired.
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19. General Structure
CREATE [OR REPLACE]
TRIGGER trigger_name
BEFORE (or AFTER)
INSERT OR UPDATE [OF COLUMNS] OR DELETE
ON tablename
[FOR EACH ROW [WHEN (condition)]]
BEGIN
END;
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20. Trigger Syntax
CREATE TRIGGER <triggerName>
BEFORE|AFTER INSERT|DELETE|UPDATE
[OF <columnList>] ON <tableName>|<viewName>
[REFERENCING [OLD AS <oldName>] [NEW AS
<newName>]]
[FOR EACH ROW] (default is “FOR EACH
STATEMENT”)
[WHEN (<condition>)]
<PSM body>;
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21. Example 1:
CREATE OR REPLACE TRIGGER
PERSON_INSERT_BEFORE
BEFORE INSERT
ON EMP
BEGIN
DBMS_OUTPUT.PUT_LINE(’BEFORE INSERT OF
’ || :NEW.NAME);
END;
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22. Example 2:
CREATE OR REPLACE TRIGGER Print_salary_changes
BEFORE DELETE OR INSERT OR UPDATE ON emp
WHEN (EMPNO > 0)
DECLARE
sal_diff number;
BEGIN
sal_diff := :NEW.SAL - :OLD.SAL;
dbms_output.put_line('Old salary: '
||:OLD.sal);
dbms_output.put_line('New salary: ' ||
:NEW.sal);
dbms_output.put_line(' Difference ' ||
sal_diff);
END; /
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