Book Image

Learning PostgreSQL 10 - Second Edition

Book Image

Learning PostgreSQL 10 - Second Edition

Overview of this book

PostgreSQL is one of the most popular open source databases in the world, supporting the most advanced features included in SQL standards. This book will familiarize you with the latest features released in PostgreSQL 10. We’ll start with a thorough introduction to PostgreSQL and the new features introduced in PostgreSQL 10. We’ll cover the Data Definition Language (DDL) with an emphasis on PostgreSQL, and the common DDL commands supported by ANSI SQL. You’ll learn to create tables, define integrity constraints, build indexes, and set up views and other schema objects. Moving on, we’ll cover the concepts of Data Manipulation Language (DML) and PostgreSQL server-side programming capabilities using PL/pgSQL. We’ll also explore the NoSQL capabilities of PostgreSQL and connect to your PostgreSQL database to manipulate data objects. By the end of this book, you’ll have a thorough understanding of the basics of PostgreSQL 10 and will have the necessary skills to build efficient database solutions.
Table of Contents (23 chapters)
Title Page
Credits
About the Authors
About the Reviewers
www.PacktPub.com
Customer Feedback
Preface

Query rewriting


Writing a query in several ways enables the developer to detect some issues in coding best practices, planner parameters, and performance optimization. The example of returning the guru IDs, names, and the count of success_stories can be written as follows: 

postgres=# \o /dev/null
postgres=# \timing 
Timing is on.
postgres=# SELECT id, name, (SELECT count(*) FROM success_story where guru_id=id) FROM guru;
Time: 144,929 ms
postgres=# WITH counts AS (SELECT count(*), guru_id FROM success_story group by guru_id) SELECT id, name, COALESCE(count,0) FROM guru LEFT JOIN counts on guru_id = id;
Time: 728,855 ms
postgres=# SELECT guru.id, name, COALESCE(count(*),0) FROM guru LEFT JOIN success_story on guru_id = guru.id group by guru.id, name ;
Time: 452,659 ms
postgres=# SELECT id, name, COALESCE(count,0) FROM guru LEFT JOIN ( SELECT count(*), guru_id FROM success_story group by guru_id )as counts on guru_id = id;
Time: 824,164 ms
postgres=# SELECT guru.id, name, count(*) FROM guru...