Join events and events to find time to first action
Last updated: December 10, 2025
Quick Overview
Write a query joining events and sessions to produce the combined time to first action.
Anduril
December 10, 202514
10
4,221 solved
Write a query joining events and sessions to produce the combined time to first action.
Data manipulation questions at Anduril test your ability to work with real-world datasets. This Phone Screen 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
- How would you handle this if the data was spread across multiple databases?
- What would you do if this query needs to run every 5 minutes?
- How would you handle slowly changing dimensions in this scenario?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we have two main datasets: 'events' and 'sessions'. The 'events' table contains individual user actions along with timestamps, while the 'sessions' table captures session information ...
Approach
- Identify Relevant Columns: From the 'events' table, we need the event timestamp and session ID. From the 'sessions' table, we need the session start time and session ID.
- Join Tables: Per...
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