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

Using advanced statement window functions

In this section, we will discuss advanced window functions in detail, and we will explore some techniques that may be useful for carrying out more detailed data analysis.

Let’s start with a query that we saw at the start of this chapter:

forumdb=> select distinct category, count(*) over (partition by category)              
from posts order by category;
 category | count
----------+-------
        1 |     2
        3 |     1
(2 rows)

Here, below, there is another way to write the same aggregate that we described before:

forumdb=> select distinct category, count(*) over w1
from posts WINDOW w1 as (partition by category RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
order by category;
 category | count
----------+-------
        1 |     2
        3 |     1
(2 rows)

What does RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW mean? They are the default conditions, known as the frame clause. This means that...