Join rides and messages to find average revenue

Last updated: February 24, 2026

Quick Overview

Write a query joining rides and products to produce the combined average revenue.

Grubhub
Data Manipulation (SQL/Python)
Data Scientist
Grubhub
February 24, 2026
Data Scientist
Phone Screen
Data Manipulation (SQL/Python)
Medium

20

7

3,324 solved

Write a query joining rides and products to produce the combined average revenue.

This question from Grubhub's Phone 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
  • 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
Subqueries and correlated subqueries
Window functions (ROW_NUMBER, RANK, LAG, LEAD)
Data cleaning and transformation
Index optimization and query performance
How to Approach This
  1. Clarify the schema and expected output format before writing queries.
  2. Use CTEs (WITH clauses) to break complex queries into readable steps.
  3. Consider window functions (ROW_NUMBER, RANK, LAG, LEAD) for ranking and sequential analysis.
  4. Watch for NULLs, duplicates, and edge cases in JOINs and GROUP BY.
  5. For pandas, prefer vectorized operations over row-by-row iteration.
Possible Follow-up Questions
  • Can you rewrite this without using subqueries?
  • How would you validate the correctness of your query results?
  • How would you handle slowly changing dimensions in this scenario?
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Practice SQL Problems
Sample Answer
Problem Understanding

In this problem, we have two tables: rides and products. The rides table contains information about rides taken, including ride IDs, user IDs, and revenue generated from each ride. The `products...

Approach

To solve this problem, I would take the following steps:

  1. Join the Tables: Use an INNER JOIN to combine the rides and products tables on the ride ID to access revenue from both sources.
  2. *...
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Grubhub Data Scientist Interview Guide

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