Book Image

Mastering PostgreSQL 15 - Fifth Edition

By : Hans-Jürgen Schönig
Book Image

Mastering PostgreSQL 15 - Fifth Edition

By: Hans-Jürgen Schönig

Overview of this book

Starting with an introduction to the newly released features of PostgreSQL 15, this updated fifth edition will help you get to grips with PostgreSQL administration and how to build dynamic database solutions for enterprise apps, including designing both physical and technical aspects of the system. You'll explore advanced PostgreSQL features, such as logical replication, database clusters, advanced indexing, and user management to manage and maintain your database. You'll then work with the PostgreSQL optimizer, configure PostgreSQL for high speed, and move from Oracle to PostgreSQL. Among the other skills that the book will help you build, you’ll cover transactions, handling recursions, working with JSON and JSONB data, and setting up a Patroni cluster. It will show you how to improve performance with query optimization. You'll also focus on managing network security and work with backups and replication while exploring useful PostgreSQL extensions that optimize the performance of large databases. By the end of this PostgreSQL book, you’ll be able to use your database to its utmost capacity by implementing advanced administrative tasks with ease.
Table of Contents (16 chapters)

Making use of ordered sets

Ordered sets are powerful features but are not widely regarded as such and are not widely known in the developer community. The idea is actually quite simple: data is grouped normally, and then the data inside each group is ordered given a certain condition. The calculation is then performed on this sorted data.

A classic example is the calculation of the median.

Important note

The median is the middle value. For example, if you are earning the median income, the numbers of people earning less and more than you are identical: 50% of people are earning more and 50% of people are earning less.

One way to get the median is to take sorted data and move 50% into the dataset. This is an example of what the WITHIN GROUP clause will ask PostgreSQL to do:

test=# SELECT region,
    percentile_disc(0.5) WITHIN GROUP (ORDER BY production)
FROM t_oil
GROUP BY 1;
 region         | percentile_disc...