Write a query to find time to first action from messages
Last updated: August 9, 2025
Quick Overview
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
Anduril
August 9, 20250
7
4,518 solved
Write a SQL query to calculate time to first action from the messages table, considering nulls and duplicates.
This question from Anduril'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 this if the data was spread across multiple databases?
- How would you validate the correctness of your query results?
- What would you do if this query needs to run every 5 minutes?
- How would you handle slowly changing dimensions in this scenario?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to calculate the 'time to first action' from a 'messages' table. This table likely contains records of user interactions, where each message may have associated timestamps for actions take...
Approach
- Identify Relevant Data: Start by selecting necessary columns from the messages table, such as message_id, created_at (timestamp of when the message was sent), and action_timestamp (timestamp of...
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