Calculate DAU/MAU ratio per user

Last updated: July 17, 2025

Quick Overview

Write a query to compute DAU/MAU ratio grouped by region, handling edge cases like nulls and duplicates.

Grafana Labs

Data Manipulation (SQL/Python)

Data Scientist

Grafana Labs

July 17, 2025

Data Scientist

Take-home Project

Data Manipulation (SQL/Python)

Medium

3,964 solved

Write a query to compute DAU/MAU ratio grouped by region, handling edge cases like nulls and duplicates.

Grafana Labs asks this during the Take-home Project 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

Aggregate functions and GROUP BY

JOIN types and when to use each

Index optimization and query performance

Window functions (ROW_NUMBER, RANK, LAG, LEAD)

Subqueries and correlated subqueries

Data cleaning and transformation

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 validate the correctness of your query results?
Can you rewrite this without using subqueries?
How would you optimize this query for a table with 100 million rows?

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Practice SQL Problems

Sample Answer

Problem Understanding

To compute the Daily Active Users (DAU) and Monthly Active Users (MAU) ratio grouped by region, we need to work with user activity data that contains timestamps, user IDs, and regional information. Th...

Approach

Identify Data Sources: Assume we have a table user_activity with columns user_id, activity_date, and region.
Extract DAU: Use a CTE (Common Table Expression) to compute the numbe...

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Grafana Labs Data Scientist Interview Guide

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