Calculate DAU/MAU ratio per product
Last updated: January 2, 2026
Quick Overview
Write a query to compute DAU/MAU ratio grouped by region, handling edge cases like nulls and duplicates.
Snapchat
January 2, 2026254
9
1,402 solved
Write a query to compute DAU/MAU ratio grouped by region, handling edge cases like nulls and duplicates.
Snapchat asks this during the Phone Screen because data engineering skills are critical for the role. You should be comfortable with complex joins, window functions, CTEs, and performance optimization.
What the Interviewer Expects
- Write syntactically correct SQL with proper JOIN and WHERE clauses
- Use GROUP BY and aggregate functions appropriately
- Handle NULL values correctly in your queries
- Explain the query execution plan at a high level
Key Topics to Cover
How to Approach This
- Clarify the schema and expected output format before writing queries.
- Use CTEs (WITH clauses) to break complex queries into readable steps.
- Consider window functions (ROW_NUMBER, RANK, LAG, LEAD) for ranking and sequential analysis.
- Watch for NULLs, duplicates, and edge cases in JOINs and GROUP BY.
- For pandas, prefer vectorized operations over row-by-row iteration.
Possible Follow-up Questions
- What indexes would you create to support this query?
- How would you handle this if the data was spread across multiple databases?
- How would you handle slowly changing dimensions in this scenario?
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