Calculate time to first action per user
Last updated: December 18, 2025
Quick Overview
Write a query to compute time to first action grouped by date, handling edge cases like nulls and duplicates.
Shopify
December 18, 202536
7
1,003 solved
Write a query to compute time to first action grouped by date, handling edge cases like nulls and duplicates.
Data manipulation questions at Shopify 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
- 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
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 indexes would you create to support this query?
- 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?
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Practice SQL ProblemsSample Answer
Problem Understanding
The task is to compute the time it takes for each user to perform their first action, grouped by the date of that action. The data involved likely includes a user identifier, a timestamp for each acti...
Approach
- Identify Relevant Tables: Start by determining the table that contains user actions, ensuring it includes user IDs and action timestamps.
- Filter for First Actions: Use a subquery to rank...
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