Join clicks and rides to find average revenue
Last updated: January 5, 2026
Quick Overview
Write a query joining clicks and transactions to produce the combined average revenue.
Doordash
January 5, 2026121
15
3,991 solved
Write a query joining clicks and transactions to produce the combined average revenue.
Data manipulation questions at Doordash test your ability to work with real-world datasets. This Take-home Project question evaluates your SQL proficiency, understanding of data modeling, and ability to derive insights from raw data.
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
- Can you rewrite this without using subqueries?
- What would you do if this query needs to run every 5 minutes?
- How would you handle this if the data was spread across multiple databases?
- How would you validate the correctness of your query results?
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Practice SQL ProblemsSample Answer
Problem Understanding
To solve the problem, we need to work with two datasets: clicks and transactions. The clicks dataset contains information about user interactions with the platform, and the *transactions...
Approach
- Identify Key Columns: Determine the common keys for joining the datasets. Typically, this will be a user ID or session ID present in both tables.
- Join the Datasets: Use an INNER JOIN to ...
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