Optimize a slow query on products
Last updated: May 15, 2026
Quick Overview
A query on products is running slowly. Identify the bottleneck and optimize it.
ServiceNow
May 15, 2026130
6
2,747 solved
A query on products is running slowly. Identify the bottleneck and optimize it.
ServiceNow 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
- Solve complex analytical problems with elegant, readable SQL
- Optimize queries for large-scale datasets with partitioning and indexing
- Use recursive CTEs, lateral joins, and advanced window functions
- Design the data model alongside the query solution
- Discuss trade-offs between SQL and programmatic approaches (Python/pandas)
- Consider the operational aspects: query scheduling, incremental processing
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 indexes would you create to support this query?
- How would you validate the correctness of your query results?
- What would you do if this query needs to run every 5 minutes?
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Practice SQL ProblemsSample Answer
Problem Understanding
In this scenario, we are tasked with optimizing a slow SQL query that operates on a dataset of products. The primary data involved includes a 'products' table that likely contains columns such as 'pro...
Approach
To optimize the query, follow these steps:
- Analyze the existing query: Identify the tables involved, the JOIN types used, filtering conditions, and date manipulations.
- **Check execution plan...
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