Optimize a slow query on products
Last updated: August 9, 2025
Quick Overview
A query on products is running slowly. Identify the bottleneck and optimize it.
Figma
Data Manipulation (SQL/Python)
Data Scientist
Figma
August 9, 2025Data Scientist
Technical Screen
Data Manipulation (SQL/Python)
Easy
10
6
3,540 solved
A query on products is running slowly. Identify the bottleneck and optimize it.
Figma asks this during the Technical Screen 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
Pandas vectorized operations and groupby
JOIN types and when to use each
NULL handling and COALESCE
Common Table Expressions (CTEs)
Date/time manipulation
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 handle slowly changing dimensions in this scenario?
- How would you handle this if the data was spread across multiple databases?
- What indexes would you create to support this query?
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Practice SQL ProblemsSample Answer
Problem Understanding
The query needs to analyze product data from a table (let's call it products) that contains information such as product ID, category, price, and creation date. The goal is to identify performance bo...
Approach
- Examine Existing Query: Review the current SQL query to identify inefficient joins, unnecessary calculations, or lack of indexing.
- Use CTEs for Clarity: Implement Common Table Expressi...
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