Calculate churn rate per region
Last updated: March 4, 2026
Quick Overview
Write a query to compute churn rate grouped by date, handling edge cases like nulls and duplicates.
Coinbase
March 4, 2026129
7
2,276 solved
Write a query to compute churn rate grouped by date, handling edge cases like nulls and duplicates.
Coinbase asks this during the Technical 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
- How would you optimize this query for a table with 100 million rows?
- What indexes would you create to support this query?
- How would you validate the correctness of your query results?
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Practice SQL ProblemsSample Answer
Problem Understanding
To calculate the churn rate per region for Coinbase, we must understand the data involved. The churn rate is typically defined as the percentage of customers who stopped using the service during a spe...
Approach
- Identify the necessary tables: We need a customer table that includes fields like
customer_id,region,status, andchurn_date. - Calculate total customers and churned customers: Us...
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