Write a query to find DAU/MAU ratio from orders
Last updated: February 8, 2026
Quick Overview
Write a SQL query to calculate DAU/MAU ratio from the orders table, considering nulls and duplicates.
Apple
February 8, 2026114
5
2,372 solved
Write a SQL query to calculate DAU/MAU ratio from the orders table, considering nulls and duplicates.
This question from Apple's Technical Screen tests practical data skills. The interviewer wants to see clean, efficient queries that handle edge cases like NULLs, duplicates, and large datasets.
What the Interviewer Expects
- Solve complex analytical problems with elegant, readable SQL
- Optimize queries for large-scale datasets with partitioning and indexing
- Use recursive CTEs, lateral joins, and advanced window functions
- Design the data model alongside the query solution
- Discuss trade-offs between SQL and programmatic approaches (Python/pandas)
- Consider the operational aspects: query scheduling, incremental processing
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
- How would you handle this if the data was spread across multiple databases?
- Can you rewrite this without using subqueries?
- How would you optimize this query for a table with 100 million rows?
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