Calculate average revenue per product
Last updated: August 21, 2025
Quick Overview
Write a query to compute average revenue grouped by region, handling edge cases like nulls and duplicates.
Oracle
August 21, 202544
5
468 solved
Write a query to compute average revenue grouped by region, handling edge cases like nulls and duplicates.
This question from Oracle's Phone Screen 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
- Can you rewrite this without using subqueries?
- 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 average revenue per product grouped by region, we need to work with a dataset that contains at least the following columns: product_id, region, and revenue. The query needs to c...
Approach
- Identify Relevant Data: Ensure we have access to the necessary columns (
product_id,region,revenue). - Handle NULLs: Use COALESCE to treat NULL revenues as 0 for the average calcu...
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