How to use MySQL Trigger

Triggers in MySQL are database objects tied to specific events that fire when a certain action occurs in the database. They can be used to automate tasks such as logging changes, enforcing business rules, and synchronizing data across tables. In this tutorial, we'll discuss how to create and use triggers in MySQL.

Syntax

The syntax to create a trigger in MySQL is as follows:

CREATE TRIGGER trigger_name
trigger_time trigger_event
ON table_name
FOR EACH ROW
BEGIN
   -- Trigger body goes here
END;

• trigger_name: The name of the trigger.
• trigger_time: The time when the trigger will be executed. This can be BEFORE or AFTER the trigger event.
• trigger_event: The event that fires the trigger. This can be INSERT, UPDATE, or DELETE.
• table_name: The name of the table that the trigger is attached to.
• BEGIN and END: The code block that will be executed when the trigger fires. This code block can contain SQL statements or call stored procedures.

Example

Let's create a trigger that logs whenever a new user is added to the users table:

CREATE TRIGGER log_new_user
AFTER INSERT
ON users
FOR EACH ROW
BEGIN
   INSERT INTO user_logs(user_id, action) VALUES(NEW.id, 'New user added');
END;

This trigger will execute after an INSERT event occurs in the users table and will log a new entry in the user_logs table.

Output

When a trigger is fired, it will execute the code block defined in the trigger body. In the above example, when a new user is added to the users table, the trigger will execute and insert a new entry into the user_logs table.

Explanation

In the example above, we created a trigger called log_new_user that will execute after an INSERT event occurs in the users table. The code block defined in the trigger body will insert a new entry in the user_logs table, recording that a new user has been added.

Use

Triggers can be used to automate various tasks in a database. They can be used to enforce data constraints, log changes, and synchronize data. Triggers can also be used to modify data in other tables when an event occurs in one table.

Important Points

• Triggers can be used to automate tasks such as logging changes, enforcing business rules, and synchronizing data across tables.
• Triggers can be created using SQL and attached to specific events on specific tables.
• Each trigger can contain a SQL statement or call a stored procedure.

Summary

In this tutorial, we explored how to create and use triggers in MySQL. We discussed the syntax, example, output, explanation, use, and important points of using triggers in MySQL. With this knowledge, you can now use triggers to automate various tasks in your MySQL database.