Optimize a slow query on orders
Last updated: November 15, 2025
Quick Overview
A query on orders is running slowly. Identify the bottleneck and optimize it.
Visa
November 15, 2025520
7
2,218 solved
A query on orders is running slowly. Identify the bottleneck and optimize it.
Visa 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
- 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 would you do if this query needs to run every 5 minutes?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice SQL ProblemsSample Answer
Problem Understanding
The query involves a table named orders which contains transactional data. We need to identify the bottleneck causing slow performance and optimize the query to improve execution time. The objective...
Approach
To optimize the query, I would follow these steps:
- Analyze the Existing Query: Review the current SQL query to identify which parts are slow (e.g., joins, WHERE clause, aggregates).
- **Index ...
Submit Your Answer
