How to create triggers for oracle

Triggers in Oracle are SQL code that is automatically executed when a specific event occurs and are used in Data Operation Language (DML) operations (such as insertion, update, or delete). The syntax for creating a trigger is: CREATE TRIGGER [trigger name] BEFORE/AFTER [trigger event] ON [table name] AS [trigger code]. Trigger events include: BEFORE INSERT, AFTER INSERT, BEFORE UPDATE, AFTER UPDATE, BEFORE DELETE, AFTER DELETE. The trigger code specifies the SQL statement executed when the trigger event occurs.

Create triggers using Oracle

What are triggers?

A trigger is a piece of SQL code that executes automatically when a specific event occurs. These events may be Data Operation Language (DML) operations, such as INSERT, UPDATE, or DELETE.

How to create a trigger

To create a trigger in Oracle, you can use the following syntax:

 <code class="sql">CREATE TRIGGER [触发器名称] BEFORE/AFTER [触发事件] ON [表名称] AS [触发器代码]</code>

Trigger Event

The trigger event specifies when the trigger will fire. Possible trigger events include:

• BEFORE INSERT : Before inserting a new row into the table
• AFTER INSERT : After inserting a new row into the table
• BEFORE UPDATE : Before updating existing rows in the table
• AFTER UPDATE : After updating existing rows in the table
• BEFORE DELETE : Before deleting rows from table
• AFTER DELETE : After deleting rows from table

Trigger code

The trigger code contains SQL statements that will be executed when the trigger event occurs. It can perform various operations, such as:

• Verify data input
• Maintain data integrity
• Track data changes
• Send notification

Example

The following example creates a trigger that validates salary before inserting a new row into the EMPLOYEES table:

 <code class="sql">CREATE TRIGGER check_salary BEFORE INSERT ON EMPLOYEES AS BEGIN IF NEW.salary </code>

The function of the trigger

Triggers are useful in the following situations:

• Enforce business rules
• Maintain data consistency
• Improve application performance
• Simplify complex database operations

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