"A query that ran perfectly during development suddenly slows down as data accumulates." At such times, the mark of a truly skilled developer is identifying the root cause based on solid evidence rather than guesswork, and optimizing a 30-second query down to 0.1 seconds. Master the core principles of database performance—from execution plans, indexes, and optimizers to joins and sorting—using millions of rows of real-world data. Elevate your skills and become a top-tier developer capable of independently analyzing and resolving slow queries in production environments.

Solve the common codes, category hierarchies, history tracking, soft deletes, statistics, dynamic design, JSON utilization, and more that you inevitably encounter in real-world design through nine core patterns. This goes beyond simple theory, incorporating practical know-how proven across numerous projects and criteria for making the right choices in different situations. Become a true design expert who can confidently design for any requirement.

Learn database design systematically across three levels—conceptual, logical, and physical—and strengthen your skills through a practical, project-based e-commerce store. Gain hands-on expertise through modern design techniques and the latest trends.

Learn the essential fundamentals of SQL and databases needed for practical work. Not only developers, but also planners and data analysts will learn SQL in depth.

Not only developers, but also planners and data analysts learn databases step by step, starting with the basics of SQL.

Learn the essential modern Java technologies of Lambda, Stream, and functional programming with Java, from the basics to the practical level, in depth.

Learn I/O, networking, reflection, and annotations in depth, from the basics to the practical level. Build a web application server (WAS) directly in Java.

This course provides an in-depth study of multithreading and concurrency, from basic principles to practical applications.

Learn Java generics and collection frameworks in depth with a focus on practical applications. Also learn the basics of data structures.

This book provides an in-depth study of various intermediate-level Java features necessary for practical work, using example code.

This is a video of the meetup that took place at 7pm on January 31st.

Learn practical core Java object-oriented concepts easily via example code.