This book systematically discusses the theory, technology, and applications of the openGauss database. The book has 11 chapters in total. It begins by introducing the history of database development, including traditional network databases, hierarchical databases, relational databases, NoSQL databases, NewSQL databases, cloud databases, multi-model databases, and distributed databases. It then covers fundamental database knowledge such as Structured Query Language (SQL), SQL syntax, stored procedures, triggers, cursors, database design specifications, and E-R models. After that, it explores the future trends of database development, including the impact of new hardware, different deployment forms, and new applications on databases. Finally, the core technologies of openGauss are highlighted, including its core architecture, optimizations for new hardware like Kunpeng and Ascend, SQL engine, actuator technology, database storage technology, database transaction mechanisms, database security, and autonomous database technology. To facilitate readers to master database teaching content, each chapter provides summaries and exercises (with answers).By reading this book, readers can gain in-depth insights into the development history and future trends of databases, database system architecture, optimization techniques for Kunpeng and Ascend, database transaction processing technology, actuator technology, and database security technology so that they can both develop the core code of databases in the future and better utilize databases for application development.This book can serve as a reference for undergraduate and graduate students studying databases and is also suitable for teachers engaged in the teaching or scientific research of database theory and researchers of system realization in institutes of higher education and research organizations. It can also be used as a reference for corporate engineers conducting secondary database development and application development.