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

Exploring CTEs

In this section, we are going to talk about CTEs. This section will be split into three parts. Firstly, we will talk about the concept of CTEs; secondly, we will discuss how CTEs are implemented starting from PostgreSQL 12; and finally, we will explore some examples of how to use CTEs.

CTE concept

A CTE, or a common table expression, is a temporary result taken from a SQL statement. This statement can contain SELECT, INSERT, UPDATE, or DELETE instructions. The lifetime of a CTE is equal to the lifetime of the query. Here is an example of a CTE definition:

WITH cte_name (column_list) AS (
 CTE_query_definition
)
statement;

If, for example, we wanted to create a temporary dataset with all the posts written by the author enrico_pirozzi, we would have to write this:

forumdb=> with posts_author_1 as
 (select p.* from posts p
 inner join users u on p.author=u.pk
 where username='enrico_pirozzi')
select pk,title from posts_author_1;
 pk |...