Join rides and messages to find cumulative sum
Last updated: April 14, 2026
Quick Overview
Write a query joining rides and impressions to produce the combined cumulative sum.
Cruise
Data Manipulation (SQL/Python)
Data Scientist
Cruise
April 14, 2026Data Scientist
Onsite
Data Manipulation (SQL/Python)
Medium
0
4
2,696 solved
Write a query joining rides and impressions to produce the combined cumulative sum.
This question from Cruise's Onsite 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
Date/time manipulation
Subqueries and correlated subqueries
Data cleaning and transformation
Common Table Expressions (CTEs)
JOIN types and when to use each
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 slowly changing dimensions in this scenario?
- What indexes would you create to support this query?
- How would you optimize this query for a table with 100 million rows?
- How would you validate the correctness of your query results?
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Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we have two tables: rides and messages. The rides table contains information about different rides, including a timestamp and a unique ride identifier. The messages table hold...
Approach
To solve this problem, we can follow these steps:
- Identify the Join Condition: We will join the tables on the ride identifier. We need to ensure that we include all rides even if they have no c...
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