Join products and impressions to find average revenue
Last updated: December 5, 2025
Quick Overview
Write a query joining products and sessions to produce the combined average revenue.
Bloomberg
December 5, 20253
7
1,344 solved
Write a query joining products and sessions to produce the combined average revenue.
This question from Bloomberg'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
- What would you do if this query needs to run every 5 minutes?
- How would you validate the correctness of your query results?
- How would you optimize this query for a table with 100 million rows?
- Can you rewrite this without using subqueries?
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