Optimize a slow query on clicks
Last updated: December 13, 2025
Quick Overview
A query on clicks is running slowly. Identify the bottleneck and optimize it.
Microsoft
Data Manipulation (SQL/Python)
Data Scientist
Microsoft
December 13, 2025Data Scientist
Phone Screen
Data Manipulation (SQL/Python)
Hard
17
6
2,993 solved
A query on clicks is running slowly. Identify the bottleneck and optimize it.
This question from Microsoft's Phone Screen tests practical data skills. The interviewer wants to see clean, efficient queries that handle edge cases like NULLs, duplicates, and large datasets.
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
Pandas vectorized operations and groupby
Index optimization and query performance
Aggregate functions and GROUP BY
JOIN types and when to use each
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 this if the data was spread across multiple databases?
- How would you handle slowly changing dimensions in this scenario?
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 problem involves optimizing a slow SQL query that aggregates click data. The relevant data is stored in a clicks table, which includes columns such as user_id, click_time, page_id, and pos...
Approach
- Identify the Query: First, review the existing SQL query to understand its structure and identify bottlenecks.
- Analyze Execution Plan: Use
EXPLAINto see how the database executes the...
Submit Your Answer
Markdown supported