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

The EXPLAIN statement

EXPLAIN is the statement that allows you to see how PostgreSQL is going to execute a specific query. You have to pass the statement you want to analyze to EXPLAIN, and the execution plan will be shown.

There are a few important things to know before using EXPLAIN:

  • It will only show the best plan, which is the one with the lowest cost among all the evaluated plans.
  • It will not execute the statement you are asking the plan for, therefore the EXPLAIN execution is fast and pretty much constant each time.
  • It will present you with all the execution nodes that the executor will use to provide you with the dataset.

Let's see an example of EXPLAIN in action to better understand. Imagine we need to understand the execution plan of the SELECT * FROM categories statement. In this case, you need to prefix the statement with the EXPLAIN command, as follows:

forumdb=> EXPLAIN SELECT * FROM categories;