Book Image

Learn PostgreSQL

By : Luca Ferrari, Enrico Pirozzi
Book Image

Learn PostgreSQL

By: Luca Ferrari, Enrico Pirozzi

Overview of this book

PostgreSQL is one of the fastest-growing open source object-relational database management systems (DBMS) in the world. As well as being easy to use, it’s scalable and highly efficient. In this book, you’ll explore PostgreSQL 12 and 13 and learn how to build database solutions using it. Complete with hands-on tutorials, this guide will teach you how to achieve the right database design required for a reliable environment. You'll learn how to install and configure a PostgreSQL server and even manage users and connections. The book then progresses to key concepts of relational databases, before taking you through the Data Definition Language (DDL) and commonly used DDL commands. To build on your skills, you’ll understand how to interact with the live cluster, create database objects, and use tools to connect to the live cluster. You’ll then get to grips with creating tables, building indexes, and designing your database schema. Later, you'll explore the Data Manipulation Language (DML) and server-side programming capabilities of PostgreSQL using PL/pgSQL, before learning how to monitor, test, and troubleshoot your database application to ensure high-performance and reliability. By the end of this book, you'll be well-versed with the Postgres database and be able to set up your own PostgreSQL instance and use it to build robust solutions.
Table of Contents (27 chapters)
Section 1: Getting Started
Section 2: Interacting with the Database
Section 3: Administering the Cluster
Section 4: Replication
Section 5: The PostegreSQL Ecosystem

Exploring rules in PostgreSQL

As mentioned earlier, rules are simple event handlers. At the user level, it is possible to manage all the events that perform write operations, which are as follows:


The fundamental concept behind rules is to modify the flow of an event. If we are given an event, what we can do when certain conditions occur is as follows:

  • Do nothing and then undo the action of that event.
  • Trigger another event instead of the default one.
  • Trigger another event in conjunction with the default.

So, given a write operation, for example, an INSERT operation, we can perform one of these three actions:

  • Cancel the operation.
  • Perform another operation instead of the INSERT.
  • Execute the INSERT and simultaneously perform another operation.

Understanding the OLD and NEW variables

Before we start working with rules and then with triggers, we need to understand the concept of the OLD and NEW variables.

The OLD and NEW variables represent the state of the row...