SELECT student_id, year, score, LAG(score) OVER (PARTITION BY student_id ORDER BY year) AS prev_year_score FROM student_scores. **LAG(score, 2)** for two years back. **Default**: First row has NULL prev. **COALESCE** for default....
This medium-level SQL question appears frequently in data engineering interviews at companies like Deolite. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (partition) 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.
SELECT student_id, year, score, LAG(score) OVER (PARTITION BY student_id ORDER BY year) AS prev_year_score FROM student_scores. LAG(score, 2) for two years back. Default: First row has NULL prev. COALESCE for default. Partition: Per-student ordering.
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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.