Book Image

Learn PostgreSQL - Second Edition

By : Luca Ferrari, Enrico Pirozzi
1 (2)
Book Image

Learn PostgreSQL - Second Edition

1 (2)
By: Luca Ferrari, Enrico Pirozzi

Overview of this book

The latest edition of this PostgreSQL book will help you to start using PostgreSQL from absolute scratch, helping you to quickly understand the internal workings of the database. With a structured approach and practical examples, go on a journey that covers the basics, from SQL statements and how to run server-side programs, to configuring, managing, securing, and optimizing database performance. This new edition will not only help you get to grips with all the recent changes within the PostgreSQL ecosystem but will also dig deeper into concepts like partitioning and replication with a fresh set of examples. The book is also equipped with Docker images for each chapter which makes the learning experience faster and easier. Starting with the absolute basics of databases, the book sails through to advanced concepts like window functions, logging, auditing, extending the database, configuration, partitioning, and replication. It will also help you seamlessly migrate your existing database system to PostgreSQL and contains a dedicated chapter on disaster recovery. Each chapter ends with practice questions to test your learning at regular intervals. By the end of this book, you will be able to install, configure, manage, and develop applications against a PostgreSQL database.
Table of Contents (22 chapters)
20
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21
Index

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, at least unless you explicitly ask for its execution. 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...