Calculate DAU/MAU ratio per date
Last updated: August 19, 2025
Quick Overview
Write a query to compute DAU/MAU ratio grouped by user, handling edge cases like nulls and duplicates.
Capital One
August 19, 202598
7
2,480 solved
Write a query to compute DAU/MAU ratio grouped by user, handling edge cases like nulls and duplicates.
Data manipulation questions at Capital One test your ability to work with real-world datasets. This Technical Screen question evaluates your SQL proficiency, understanding of data modeling, and ability to derive insights from raw data.
What the Interviewer Expects
- Use advanced SQL features: window functions, CTEs, subqueries
- Write efficient queries that avoid common performance pitfalls
- Handle complex data transformations with multiple joins and aggregations
- Discuss indexing strategy and query optimization
- Address data quality issues: duplicates, missing values, outliers
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 optimize this query for a table with 100 million rows?
- How would you handle this if the data was spread across multiple databases?
- How would you validate the correctness of your query results?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
To calculate the Daily Active Users (DAU) and Monthly Active Users (MAU) ratio per date, we need to work with a dataset containing user activity logs. The relevant columns typically include user_id,...
Approach
- CTE for DAU: Create a Common Table Expression (CTE) to calculate daily active users by selecting distinct
user_idfor eachactivity_date. - CTE for MAU: Create another CTE to calculate...
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