Write a query to find churn rate from rides
Last updated: February 12, 2026
Quick Overview
Write a SQL query to calculate churn rate from the rides table, considering nulls and duplicates.
Vercel
February 12, 2026276
5
4,173 solved
Write a SQL query to calculate churn rate from the rides table, considering nulls and duplicates.
Vercel 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
- 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
- What would you do if this query needs to run every 5 minutes?
- Can you rewrite this without using subqueries?
- How would you handle this if the data was spread across multiple databases?
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Practice SQL ProblemsSample Answer
Problem Understanding
To calculate the churn rate from the rides table, we need to understand the structure of the data involved. The rides table likely contains information about user rides, including user IDs, ride dates...
Approach
- Identify Active Users: Use a Common Table Expression (CTE) to select distinct users who have taken rides within the last month.
- Identify All Users: Create another CTE to select all disti...
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