Triggers¶

Using triggers¶

A trigger is a database object that automatically performs a specified action in response to certain events on a table or view. It allows users to enforce business rules, maintain data integrity, and automate tasks within the database.

Advantages of Using Triggers¶

Benefits	Description
Data Integrity	Triggers can enforce data integrity constraints by automatically validating or modifying data before it is inserted, updated, or deleted in a table.
Audit Trails	Triggers can be used to create audit trails by recording changes made to the database, including who made the changes and when they occurred.
Simplified	Triggers simplify application logic by moving complex business rules and validation checks into the database, reducing the amount of code needed in the application layer.
Automated	Triggers automate repetitive tasks, such as updating denormalized data or sending notifications, by executing predefined actions in response to specified events.

Disadvantages of Using Triggers¶

Disadvantages	Description
Complexity	Triggers can add complexity to the database schema and make it harder to understand and maintain, especially when dealing with multiple triggers and complex logic.
Performance	Triggers may impact database performance, particularly if they involve complex operations or are triggered frequently, leading to increased overhead and slower response times.
Debugging	Triggers can be difficult to debug and troubleshoot, as they are executed automatically in response to events and may not provide detailed error messages or logging information.
Dependency	Triggers create dependencies between database objects, making it challenging to modify or refactor the database schema without considering the impact on existing triggers.

Create a before_insert trigger¶

mysql> CREATE TRIGGER before_insert_customer
    -> BEFORE INSERT ON customers
    -> FOR EACH ROW
    -> BEGIN
    ->     SET NEW.created_at = NOW();
    -> END;

Create an after_update trigger¶

mysql> CREATE TRIGGER after_update_inventory
    -> AFTER UPDATE ON inventory
    -> FOR EACH ROW
    -> BEGIN
    ->     INSERT INTO inventory_changes (product_id, old_quantity, new_quantity, change_date)
    ->     VALUES (OLD.product_id, OLD.quantity, NEW.quantity, NOW());
    -> END;

Drop a before_insert trigger¶

mysql> DROP TRIGGER IF EXISTS before_insert_customer;

Drop an after_update trigger¶

mysql> DROP TRIGGER IF EXISTS after_update_inventory;

Advanced SQL features¶

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Last update: 2024-05-03