Calculate rolling 7-day average per date
Last updated: January 25, 2026
Quick Overview
Write a query to compute rolling 7-day average grouped by date, handling edge cases like nulls and duplicates.
Discord
January 25, 202620
3
3,654 solved
Write a query to compute rolling 7-day average grouped by date, handling edge cases like nulls and duplicates.
This question from Discord'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
- Write syntactically correct SQL with proper JOIN and WHERE clauses
- Use GROUP BY and aggregate functions appropriately
- Handle NULL values correctly in your queries
- Explain the query execution plan at a high level
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
- Can you rewrite this without using subqueries?
- How would you handle slowly changing dimensions in this scenario?
- 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?
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
We need to compute a rolling 7-day average of a specific metric (let's assume it's 'user_count') grouped by date. The data is assumed to be stored in a table called daily_users with at least two col...
Approach
- Data Preparation: Ensure that there are no NULL values in the
user_countcolumn by replacing them with 0 (or another appropriate value).
2. Aggregation: Use a window function to calc...
Submit Your Answer
