Write a query to find time to first action from messages
Last updated: September 6, 2025
Quick Overview
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
Spotify
September 6, 2025296
9
3,475 solved
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
Data manipulation questions at Spotify test your ability to work with real-world datasets. This Take-home Project question evaluates your SQL proficiency, understanding of data modeling, and ability to derive insights from raw data.
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?
- How would you validate the correctness of your query results?
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Solution Pattern
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