Write a query to find DAU/MAU ratio from users
Last updated: April 13, 2026
Quick Overview
Write a SQL query to calculate DAU/MAU ratio from the users table, considering nulls and duplicates.
Elastic
April 13, 20262
8
2,083 solved
Write a SQL query to calculate DAU/MAU ratio from the users table, considering nulls and duplicates.
Elastic 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
- 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
- Can you rewrite this without using subqueries?
- How would you validate the correctness of your query results?
- How would you handle this if the data was spread across multiple databases?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to calculate the Daily Active Users (DAU) and Monthly Active Users (MAU) ratio from a 'users' table. The 'users' table likely contains records of user activities including timestamps for w...
Approach
- Identify Unique Users: Use a SELECT DISTINCT statement to extract unique users for both DAU and MAU.
- Calculate DAU: Count distinct users per day by filtering the dataset to group by da...
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