Optimize a slow query on clicks
Last updated: January 8, 2026
Quick Overview
A query on clicks is running slowly. Identify the bottleneck and optimize it.
Adobe
Data Manipulation (SQL/Python)
Data Scientist
Adobe
January 8, 2026Data Scientist
Take-home Project
Data Manipulation (SQL/Python)
Medium
71
7
1,961 solved
A query on clicks is running slowly. Identify the bottleneck and optimize it.
Adobe asks this during the Take-home Project 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
NULL handling and COALESCE
Window functions (ROW_NUMBER, RANK, LAG, LEAD)
Subqueries and correlated subqueries
Common Table Expressions (CTEs)
Index optimization and query performance
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 handle this if the data was spread across multiple databases?
- What indexes would you create to support this query?
- How would you handle slowly changing dimensions in this scenario?
- What would you do if this query needs to run every 5 minutes?
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Practice SQL ProblemsSample Answer
Problem Understanding
The query in question involves a table containing click data, likely structured with fields such as user_id, click_time, product_id, and possibly other metrics related to the click event. The go...
Approach
- Analyze the Existing Query: Review the current SQL query to identify any performance bottlenecks. Look for expensive operations such as joins on large tables without indexes, excessive aggregat...
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