**LAG approach**: WITH t AS (SELECT date, revenue, LAG(revenue) OVER (ORDER BY date) AS prev_rev FROM sales) SELECT date, revenue FROM t WHERE revenue < prev_rev AND prev_rev IS NOT NULL. **Consecutive pairs**: Self-join ON a.date = b.date + 1 WHERE a.revenue < b.revenue. **N...
This medium-level SQL question appears frequently in data engineering interviews at companies like Uber. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join) 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.
LAG approach: WITH t AS (SELECT date, revenue, LAG(revenue) OVER (ORDER BY date) AS prev_rev FROM sales) SELECT date, revenue FROM t WHERE revenue < prev_rev AND prev_rev IS NOT NULL. Consecutive pairs: Self-join ON a.date = b.date + 1 WHERE a.revenue < b.revenue. N consecutive: Extend with multiple LAG or recursive pattern. Gaps: Date sequence must be continuous or use date diff.
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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.