Write a query to find rolling 7-day average from rides
Last updated: August 13, 2025
Quick Overview
Write a SQL query to calculate rolling 7-day average from the rides table, considering nulls and duplicates.
Discord
August 13, 20250
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4,929 solved
Write a SQL query to calculate rolling 7-day average from the rides table, considering nulls and duplicates.
This question from Discord's Take-home Project 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 optimize this query for a table with 100 million rows?
- Can you rewrite this without using subqueries?
- How would you validate the correctness of your query results?
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Practice SQL ProblemsSample Answer
Problem Understanding
The goal is to calculate the rolling 7-day average of rides from the rides table. This table likely contains columns such as ride_date, user_id, and ride_count. Notably, we need to account for...
Approach
- CTE for Daily Rides: First, create a Common Table Expression (CTE) to aggregate the total rides per day, ensuring to handle duplicates by using
SUM(ride_count)grouped byride_date. - **Ha...
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