Backend Database Interview Questions from a Current DBA Team Lead — Verify and Answer Them Directly with MySQL

When faced with a single slow query, what should you look at, what should you fix, and how can you prove it? This hands-on, 55-lesson course teaches you by setting up a virtual online store with one million orders on your local MySQL 8.0 and working directly with EXPLAIN, EXPLAIN ANALYZE, and index design.

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.

Why do requests wait when queries are fast? Locks. In a hands-on project using MySQL 8.0, Spring Boot, and JPA, reproduce record and gap locks, four types of deadlocks, long transactions and connection pool exhaustion, metadata locks during deployment, and lost updates with tests. Then fix them in code and verify the fixes with the same tests.

This is a practical backend course designed to cultivate the service planning and design thinking skills that developers need in the AI era.

We covered the concepts considered while migrating 20 billion data items managed through the existing MongoDB to MySQL.

As you work in backend development, you eventually find yourself facing a certain concern. As services multiply and traffic increases, there comes a point when simple REST communication and a CRUD-only structure begin to show their limitations. I experienced the same problem in practice and went through many trials and errors trying to balance performance with structural complexity. The solution I chose in that process was NATS. Its simple, single-binary-based setup, ultra-low-latency performance measured in microseconds, and practical feature set—from Pub/Sub and Queue Groups to JetStream—made it a highly realistic choice for actual service environments. This course is not about listing NATS’s features. Based on the problems I encountered in practice, it explains through code and workflows when and why I chose NATS and how I designed the architecture. From those new to messaging systems, to backend developers preparing for employment, and senior developers considering better architectures, this course will help everyone understand distributed systems and grow to the next level.

We enable you to fundamentally understand and resolve issues where Hangeul appears broken on web pages or in databases, or files contain unknown characters.

Drawing from my own experience of feeling despondent when trying to implement practical code during my first MSA transition—despite knowing the theory—I will help you grow into a developer who guarantees perfect data consistency amidst any system failure by directly rolling back daunting compensation logic through 9-step practical patterns and AI Agent coding.

We will develop a MSA delivery application using Docker, Docker compose, and Traefik server. In addition, we will systematically learn theoretical knowledge such as MSA, Proxy Server, Load Balancer, API Gateway, etc. that are necessary for development. All learning courses are composed of practical training, and through this, you will gain confidence in developing Docker-based applications.

This course implements a bulletin board CRUD using Spine, following the entire process from start to finish to see exactly which rules and sequences Spine uses to execute requests and complete responses. Based on Spine's core Execution Pipeline, we will examine the entire request lifecycle without omission: Routing (Handler selection) → Argument Resolution (Argument Resolver) → Controller Invocation (Invoker) → Return Value Processing (ReturnValue Handler). The focus is not on building features quickly. Instead, by directly tracing questions like "When is this logic executed?" and "Who is responsible for this step?" within Spine's architecture, you will develop the intuition to explain and control the execution flow. We also cover how cross-cutting concerns, such as logging, are separated from the controller and integrated into the execution flow (Interceptor). By the end of the bulletin board example, you will have gained something more important than just building CRUD with Spine: the criteria to determine where to attach specific features based on Spine's execution model. This is not just a simple CRUD course; it is the essential first course to truly getting started with Spine.

In this lecture, you will learn about AWS ECS, one of the representative technologies of Container Orchestration! You will also build CICD with Github Action. However, you will not learn ECS from the beginning. ECS can be called the king of DevOps, so it can feel too difficult. So, in the beginning of the lecture, we will first cover the basics with AWS Lightsail, which has a relatively low learning curve among traditional virtual servers. You will also experience the limitations and inconveniences of the existing method. By building up with the basics and “Why” in this way, you will naturally learn Docker Containers and ECS!

Does game backend development feel daunting and vague? With know-how gained from firsthand experience with numerous projects, I will show you how to perfectly integrate complex Firebase features into actual games. We will connect Firebase to a Unity 6 Watermelon Game to implement online features such as login, cloud database (Firestore) save/load, rankings, bulletin boards, and mailboxes. This is a practical course that also covers security rules, Remote Config operations, and code design based on a layered architecture (UI, logic, and data access).

From Docker, Kubernetes to microservices, CI/CD, and service mesh, you can easily learn not only the basic theory but also the actual application implementation through examples. By organizing only the core contents necessary for actual use, it provides a starting point for learning about the element technologies covered in the lecture.

Learn common components of global-scale services through popular papers, books, and articles.

This course goes beyond basic CRUD-level database usage, helping you develop the PostgreSQL skills needed in the AI era from a practical, real-world perspective. Drawing on AI development experience in Silicon Valley, you’ll gradually learn how to design and use JSON, indexes, transactions, and pgvector in actual services, while gaining the skills to solve complex data structure and performance problems.

You can quickly experience the process of deploying a sample e-commerce service to AWS and continuously improving it into a robust and efficient environment.

This course takes you from the fundamentals to advanced, real-world container workflows using Docker and Kubernetes. You will start by learning containers from the ground up, understanding how Docker works and why it is widely used in modern DevOps environments. You’ll run Docker, Docker Compose, and Kubernetes locally to improve software development, testing, and deployment workflows.

SQL data analysis! We will teach you how to solve practical problems that are applicable in the field, quickly and easily!

I have summarized the essential SQL SELECT statements and basic usage of Google Sheets that I learned while working as an analyst at a service company.

Introduction to SQL Data Analysis! Quick and easy to understand with practical problem solving!