Join events and messages to find time to first action
Last updated: December 31, 2025
Quick Overview
Write a query joining events and transactions to produce the combined time to first action.
Goldman Sachs
December 31, 202534
7
3,759 solved
Write a query joining events and transactions to produce the combined time to first action.
This question from Goldman Sachs's Technical 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
- 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
- How would you handle slowly changing dimensions in this scenario?
- How would you validate the correctness of your query results?
- What indexes would you create to support this query?
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Practice SQL ProblemsSample Answer
Problem Understanding
The problem involves two main datasets: events and transactions. The events table contains records of various user actions with timestamps, while the transactions table logs specific t...
Approach
To tackle this problem, we can follow these steps:
- Identify First Actions: Use window functions to find the first event and the first transaction for each user.
- Join the Datasets: Perfor...
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