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Triggers

What Are Triggers in PostgreSQL?

A trigger is a special kind of function that automatically runs in response to a specific event on a table. That event could be an INSERT, UPDATE, or DELETE—and the trigger can be set to run before or after the event occurs.

In PostgreSQL, triggers are paired with trigger functions, which define exactly what should happen when the trigger is fired.

Why Use Triggers?

Triggers are a powerful way to enforce rules, streamline workflows, and reduce human error. They allow you to:

  • Automatically maintain audit logs of data changes

  • Keep data in sync across related tables

  • Prevent or correct invalid data before it’s committed

  • Send notifications or log events when key actions happen

  • Enforce business logic without relying on the application layer

Because they run within the database, triggers ensure that certain behaviors always happen—regardless of which application or user is making the changes.

Real-World Use Cases

Triggers are used in many industries and systems, including:

  • Finance: Automatically logging every change to a transaction record

  • Healthcare: Enforcing patient record updates only during business hours

  • E-commerce: Updating inventory levels after an order is placed

  • CRM systems: Sending a notification when a lead is marked as "closed"

  • Data warehousing: Copying changes to a historical log table

Triggers can help you move logic closer to the data, improving both performance and consistency.

What You’ll Learn in This Section

This part of the documentation will guide you through the core concepts and syntax for working with triggers in PostgreSQL. Topics include:

  • Introduction to Triggers – What they are and how they work

  • Use Cases – Common patterns and when to use them

  • Row-level vs. Statement-level Triggers – When each type is appropriate

  • CREATE TRIGGER – The syntax for setting up triggers

  • BEFORE, AFTER, and INSTEAD OF Triggers – How timing affects behavior

  • Writing Trigger Functions – Using PL/pgSQL to define what the trigger does

  • Performance Considerations – Avoiding unnecessary slowdowns

  • Debugging Triggers – How to troubleshoot when something goes wrong

You’ll also see examples of common trigger setups, along with best practices for keeping your triggers manageable and efficient.