Introduction to MySQL Triggers

What Are MySQL Triggers?

A trigger is a database object associated with a table that activates automatically in response to specific data modification events.

These events include INSERT, UPDATE, and DELETE operations on the table.

• Triggers execute predefined SQL code automatically.
• They can be set to run BEFORE or AFTER the triggering event.
• Triggers help enforce complex business rules at the database level.

Types of Triggers in MySQL

MySQL supports triggers that fire before or after data changes.

Understanding when to use BEFORE or AFTER triggers is important for correct behavior.

• BEFORE triggers execute before the data modification happens, allowing you to modify or validate data.
• AFTER triggers execute after the data modification, useful for logging or cascading changes.

Basic Syntax for Creating a Trigger

Creating a trigger in MySQL involves specifying the timing, event, target table, and the SQL statements to execute.

The general syntax includes the CREATE TRIGGER statement followed by trigger details.

• Use CREATE TRIGGER trigger_name BEFORE|AFTER INSERT|UPDATE|DELETE ON table_name
• Define the trigger body with BEGIN ... END containing SQL statements
• Triggers execute automatically without explicit calls

Example: Creating a Simple BEFORE INSERT Trigger

This example shows a trigger that sets a timestamp column automatically before inserting a new row.