Procedure vs Trigger

When dealing with CRUD operations (Create, Read, Update, Delete) in database systems, the choice between triggers and procedures depends on the specific use case and requirements. Here's a comparison to help you decide when to use each:

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1. Triggers: Event-Driven Automation

Triggers are automatically invoked by specific events (e.g., INSERT, UPDATE, or DELETE) on a table. They are best suited for scenarios requiring automated and immediate actions without explicit calls.

When to Use Triggers:

Audit Trails: Automatically log changes to a table (e.g., who updated a record and when).

Complex Validations: Enforce business rules automatically before or after a database operation.

Derived Data Updates: Update dependent columns or tables when a primary record is modified.

Event Chaining: Perform actions like sending notifications or cascading updates.

Example: Audit Log Trigger

CREATE OR REPLACE TRIGGER log_salary_changes
AFTER UPDATE OF salary ON employees
FOR EACH ROW
BEGIN
INSERT INTO salary_audit (employee_id, old_salary, new_salary, change_date)
VALUES (:OLD.employee_id, :OLD.salary, :NEW.salary, SYSDATE);
END;

Use Case: Tracks salary updates without requiring developers to explicitly call any procedure.

Advantage: Fully automated, reducing developer intervention.

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1. Procedures: Reusable and Explicit Logic

Procedures are manually invoked blocks of code that can encapsulate logic for multiple operations. They provide more control and are best for complex or reusable business logic.

When to Use Procedures:

Explicit Operations: When an operation needs to be triggered by application code, not automatically.

Reusability: Logic that can be reused across different applications or modules (e.g., updating multiple records based on a condition).

Modularity: Break down complex workflows into manageable pieces for maintainability.

Complex Transactions: Encapsulate multiple operations (e.g., validating, updating, and logging) in a single call.

Example: Salary Update Procedure

CREATE OR REPLACE PROCEDURE update_salary(emp_id IN NUMBER, new_salary IN NUMBER) IS
BEGIN
UPDATE employees SET salary = new_salary WHERE employee_id = emp_id;
INSERT INTO salary_audit (employee_id, old_salary, new_salary, change_date)
VALUES (emp_id, (SELECT salary FROM employees WHERE employee_id = emp_id), new_salary, SYSDATE);
END;

Use Case: Updates the salary and logs the change explicitly when the procedure is called.

Advantage: Explicit and reusable across multiple modules, ensuring consistent logic.

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Conclusion

Use triggers for automated tasks like audit logging, enforcing rules, or cascading updates.

Use procedures for explicit operations that require modularity, reusability, and more complex workflows.

For most CRUD operations in enterprise systems, procedures are preferred because they offer better control, maintainability, and performance monitoring. However, triggers are indispensable when automation is a priority.