Calculate Monthly Restaurant Sales Growth
Last updated: July 27, 2026
Quick Overview
Calculate the monthly sales growth for a restaurant based on sales data provided over a period of time.
DoorDash
July 27, 20264
0
31 solved
Calculate the monthly sales growth for a restaurant based on sales data provided over a period of time.
This question is typically asked during the technical screen for a Data Scientist role at DoorDash to assess the candidate's ability to manipulate and analyze sales data using SQL or Python. The interviewer is evaluating the candidate's understanding of time series analysis, data aggregation, and their ability to derive meaningful insights from raw data.
What the Interviewer Expects
- Explain the importance of calculating sales growth.
- Demonstrate proficiency in SQL or Python for data manipulation.
- Provide a clear approach to aggregating monthly sales data.
- Calculate the growth percentage accurately.
- Discuss potential data quality issues and how to handle them.
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 missing data in the sales records?
- What other metrics would you consider for evaluating restaurant performance?
- Can you explain how seasonality might affect sales growth calculations?
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Practice SQL ProblemsSample Answer
Framing
To calculate monthly restaurant sales growth, we first need to aggregate the sales data on a monthly basis. This will allow us to compare sales figures from one month to the next and determine the gro...
Approach
- Data Aggregation: Use SQL or Python to group the sales data by month and sum the sales amounts.
- Calculate Growth: For each month, calculate the growth compared to the previous month usin...
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