Basic React.js concepts include components, props, and state. Next.js adds SSR and routing with React Hooks for logic reuse. Node.js with Express handles backend APIs using routing and various middleware types—application-level, router-level, error-handling, and built-in. PostgreSQL, a powerful RDBMS, supports complex SQL queries like fetching the 3rd highest salary using LIMIT and OFFSET or subqueries for ranking.
