Optimize a slow query on transactions
Last updated: December 25, 2025
Quick Overview
A query on transactions is running slowly. Identify the bottleneck and optimize it.
Adobe
December 25, 20257
10
3,711 solved
A query on transactions is running slowly. Identify the bottleneck and optimize it.
Adobe asks this during the Onsite 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
- 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 validate the correctness of your query results?
- How would you handle slowly changing dimensions in this scenario?
- How would you handle this if the data was spread across multiple databases?
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Solution Pattern
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