Calculate average revenue per user
Last updated: December 22, 2025
Quick Overview
Write a query to compute average revenue grouped by date, handling edge cases like nulls and duplicates.
Expedia
December 22, 2025260
6
2,298 solved
Write a query to compute average revenue grouped by date, handling edge cases like nulls and duplicates.
This question from Expedia'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
- 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 handle slowly changing dimensions in this scenario?
- How would you validate the correctness of your query results?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
To calculate the average revenue per user grouped by date, we need to work with a dataset that likely includes user transactions with corresponding revenues and timestamps. We will assume there is a `...
Approach
- Select Necessary Data: Start by selecting the date, user, and revenue from the transactions table.
- Filter NULLs: Use a WHERE clause to filter out any rows where
revenueis NULL, as the...
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