SQL Query for 2nd Highest Salary without Using MAX()

2nd highest without MAX: SELECT salary FROM employees e1 WHERE 1 = (SELECT COUNT(DISTINCT salary) FROM employees e2 WHERE e2.salary > e1.salary). Or: SELECT MIN(salary) FROM (SELECT salary FROM employees ORDER BY salary DESC LIMIT 2) t. Or DENSE_RANK: WITH r AS (SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) rn FROM employees) SELECT salary FROM r WHERE rn=2. Why it matters: Design choices compound at scale—wrong approach can cause 100× overhead. Scalability trade-offs: Profile before optimizing; validate on sample then full. Cost implications: Suboptimal choices multiply at billion-row scale.