I realized firsthand that without a solid grasp of databases, backend development becomes challenging. But you're on the right path by focusing on data first. Once you're confident in database design, security, and optimization, everything else will feel much easier.

Core Database Concepts
Relational vs. NoSQL Databases – Understanding when to use SQL (PostgreSQL, MySQL) vs. NoSQL (MongoDB, Redis).
Schema Design & Normalization – Avoiding redundancy and ensuring efficiency.
Indexes & Query Optimization – Speeding up queries and reducing load times.

1. Transactions & Concurrency ACID Properties – Ensuring reliability in SQL databases. Isolation Levels – Handling multiple transactions safely.
2. Scalability & Performance Partitioning & Sharding – Distributing data across multiple servers. Replication & High Availability – Keeping databases available under heavy load.
3. Security Best Practices SQL Injection Prevention – Protecting against common attacks. Role-Based Access Control (RBAC) – Managing user permissions securely. Data Encryption & Backup Strategies – Ensuring data safety.
4. Real-World Applications Hands-on projects with real-world database architectures. Writing optimized queries for stock/finance-related data (since you're preparing for finance-based interviews).