Implementing Triggers for Business Rules

Introduction

Triggers are automated actions in a database that execute in response to certain events. They play a crucial role in enforcing business rules and ensuring data integrity.

Key Concepts

Step-by-Step Process

Follow these steps to implement a trigger for a business rule.

CREATE TRIGGER trigger_name
BEFORE INSERT ON table_name
FOR EACH ROW
BEGIN
    -- Trigger logic here
END;
        

Example: Implementing a Trigger

Suppose we want to ensure that the salary of an employee cannot be set below 30000 during an INSERT operation.

CREATE TRIGGER check_salary
BEFORE INSERT ON employees
FOR EACH ROW
BEGIN
    IF NEW.salary < 30000 THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Salary cannot be below 30000';
    END IF;
END;
        

Best Practices

• Keep triggers simple and focused on a single task.
• Test triggers thoroughly to prevent unintended consequences.
• Avoid using triggers for complex logic that can be handled in application code.
• Document the purpose and logic of your triggers for future reference.

Flowchart of Trigger Implementation

graph TD;
    A[Start] --> B{Event Occurs};
    B -->|INSERT| C[Execute BEFORE Trigger];
    B -->|UPDATE| D[Execute AFTER Trigger];
    B -->|DELETE| E[Audit Data];
    C --> F[Check Business Rules];
    D --> F;
    E --> F;
    F --> G{Rules Valid?};
    G -->|Yes| H[Commit Changes];
    G -->|No| I[Rollback Changes];
        

FAQ