Triggers are stored programs that automatically execute when a triggering event occurs, like an insert, update, or delete statement or a system event. They have three parts - an event that activates the trigger, an optional condition to check if the trigger should run, and an action that specifies what code is executed. Common trigger types include DML triggers for data modification statements, DDL triggers for data definition statements, and logon triggers. Triggers are defined using CREATE TRIGGER syntax and can check for and prevent actions like decreasing a salary value.

1. Triggers
Group Members:
Awais Masood
Asad Azad
Sharoze

2. Triggers
• Named SQL blocks Which are Stored in Database
• Specialized Stored Proggrams which execute implicitly
• when a triggering event occurs
• Three parts:
– Event (activates the trigger)
– Condition (tests whether the triggers should run) [Optional]
– Action (what happens if the trigger runs)
• Semantics:
– When event occurs, and condition is satisfied,
– the action is performed.

3. Events
•A DML Statments
•A DDL Statments
•A System events

4. Types
• DML triggers
• DDL Triggers
• System/Database Event Triggers
• Logon Triggers
• Compound Triggers

5. 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>;

6. Example Trigger
CREATE TRIGGER minSalary
BEFORE UPDATE ON Professor
REFERENCING OLD AS oldTuple NEW as newTuple
FOR EACH ROW
WHEN (newTuple.salary < oldTuple.salary)
BEGIN
RAISE_APPLICATION_ERROR (-20004, ‘Salary Decreasing !!’);
END;
.
run;

7. Uses
• Complex Auditing
• Automatic Generates Value
• Replica / Duplicate data