Calculate average revenue per region
Last updated: September 5, 2025
Quick Overview
Write a query to compute average revenue grouped by user, handling edge cases like nulls and duplicates.
Plaid
September 5, 20252
6
3,047 solved
Write a query to compute average revenue grouped by user, handling edge cases like nulls and duplicates.
This question from Plaid's Take-home Project tests practical data skills. The interviewer wants to see clean, efficient queries that handle edge cases like NULLs, duplicates, and large datasets.
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 handle this if the data was spread across multiple databases?
- How would you handle slowly changing dimensions in this scenario?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
To compute the average revenue per region grouped by user, we need to extract relevant data from the database. The data involved includes user identifiers, revenue figures, and regional identifiers. T...
Approach
- Identify Relevant Tables: We need to determine which tables contain user information, revenue data, and regional identifiers. Let's assume we have a table named
user_revenuewith columns `use...
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