Join events and transactions to find rolling 7-day average
Last updated: February 2, 2026
Quick Overview
Write a query joining events and products to produce the combined rolling 7-day average.
Notion
February 2, 202610
6
3,334 solved
Write a query joining events and products to produce the combined rolling 7-day average.
Notion asks this during the Onsite because data engineering skills are critical for the role. You should be comfortable with complex joins, window functions, CTEs, and performance optimization.
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 optimize this query for a table with 100 million rows?
- How would you handle slowly changing dimensions in this scenario?
- How would you validate the correctness of your query results?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we are dealing with two tables: events and transactions. The events table contains records of user interactions (e.g., clicks, views) with products over time, while the `transac...
Approach
To solve this, we can follow these steps:
- Join the Tables: Use an INNER JOIN to combine
eventsandtransactionson the product ID, ensuring we only consider relevant records. - **Aggregate...
Submit Your Answer
