Write a query to find cumulative sum from rides
Last updated: September 20, 2025
Quick Overview
Write a SQL query to calculate cumulative sum from the rides table, considering nulls and duplicates.
JPMorgan
September 20, 20252
5
3,086 solved
Write a SQL query to calculate cumulative sum from the rides table, considering nulls and duplicates.
JPMorgan 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
- How would you validate the correctness of your query results?
- What would you do if this query needs to run every 5 minutes?
- What indexes would you create to support this query?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
The data involved in this problem is sourced from the 'rides' table, which contains records of individual rides including fields such as ride_id, user_id, ride_date, and ride_amount. The goal is to ca...
Approach
To build the query, we will follow these steps:
- Data Cleaning: First, we will filter out NULL values in the ride_amount column using COALESCE to replace NULLs with 0.
- Remove Duplicates: ...
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