Book Image

Mastering PostgreSQL 10

Book Image

Mastering PostgreSQL 10

Overview of this book

PostgreSQL is an open source database used for handling large datasets (big data) and as a JSON document database. This book highlights the newly introduced features in PostgreSQL 10, and shows you how you can build better PostgreSQL applications, and administer your PostgreSQL database more efficiently. We begin by explaining advanced database design concepts in PostgreSQL 10, along with indexing and query optimization. You will also see how to work with event triggers and perform concurrent transactions and table partitioning, along with exploring SQL and server tuning. We will walk you through implementing advanced administrative tasks such as server maintenance and monitoring, replication, recovery, high availability, and much more. You will understand common and not-so-common troubleshooting problems and how you can overcome them. By the end of this book, you will have an expert-level command of advanced database functionalities and will be able to implement advanced administrative tasks with PostgreSQL 10.
Table of Contents (15 chapters)

Writing your own aggregates

In this book, you can see most of the on-board functions provided by PostgreSQL. However, what SQL provides might not be enough for you. The good news is that it is possible to add your own aggregates to the database engine. In this section, you will learn how that can be done.

Creating simple aggregates

For the purpose of this example, the goal is to solve a very simple problem: if a customer takes a taxi, they usually have to pay for getting in the taxi—for example, €2.50. Then, let us assume that for each kilometer, the customer has to pay €2.20. The question now is: what is the total price of a trip?

Of course, this example is simple enough to solve without a custom aggregate...