Data & Machine Learning
SQL & Analytics
6 practice questions. Free questions open a full answer guide; the rest unlock with Pro.
- When would you reach for a SQL window function instead of GROUP BY, and how do ROW_NUMBER, RANK, and DENSE_RANK differ?
- What is the difference between a GROUP BY aggregation and a window function in SQL? Give an example where you'd reach for a window function.Go Pro
- A teammate wrote a deduplication query using GROUP BY with a long list of aggregates to collapse duplicate event rows. Walk me through when you'd reach for a window function like ROW_NUMBER() instead, and the trade-offs.Go Pro
- An analytics query that joins a large fact table to a dimension has suddenly gotten 10x slower, and the profiler shows one task running far longer than the rest. How do you diagnose and fix it?Go Pro
- Describe what a SQL JOIN does. What is the difference between INNER JOIN and LEFT JOIN?Go Pro
- Given a table that may contain duplicate rows, how would you find the duplicates and keep only one row per key in SQL?Go Pro
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