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

Using basic statement window functions

As we saw in the previous chapter, aggregation functions behave in the following way:

The data is first sorted and then aggregated; the data is then flattened through aggregation. This is what happens when we execute the following statement:

forumdb=# select category,count(*) from posts group by category order by category;

Alternatively, we can decide to use window functions by executing the following statement:

forumdb=# select category, count(*) over (partition by category) from posts order by category;
category | count
10 | 1
11 | 3
11 | 3
11 | 3
12 | 1
(5 rows)

Window functions create aggregates without flattening the data into a single row. However, they replicate it for all the rows to which the grouping functions refer. The behavior of PostgreSQL is depicted in the following diagram:

This is the reason that the distinct keyword has to be added to the preceding query if we want to obtain the...