**Window:** AVG(salary) OVER (PARTITION BY department_id). No GROUP BY needed—each row gets dept avg. Compare to overall: AVG(salary) OVER (). SELECT employee_id, name, salary, AVG(salary) OVER (PARTITION BY department_id) AS dept_avg FROM employees;
This medium-level SQL question appears frequently in data engineering interviews at companies like HashedIn. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (partition, window) will help you answer variations of this question confidently.
Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.
Window: AVG(salary) OVER (PARTITION BY department_id). No GROUP BY needed—each row gets dept avg. Compare to overall: AVG(salary) OVER ().
SELECT employee_id, name, salary,
AVG(salary) OVER (PARTITION BY department_id) AS dept_avg
FROM employees;
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Analyze My Answer — FreeAccording to DataEngPrep.tech, this is one of the most frequently asked SQL interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.