Join rides and orders to find conversion rate
Last updated: August 21, 2025
Quick Overview
Write a query joining rides and products to produce the combined conversion rate.
PayPal
Data Manipulation (SQL/Python)
Data Scientist
PayPal
August 21, 2025Data Scientist
Technical Screen
Data Manipulation (SQL/Python)
Medium
42
5
2,295 solved
Write a query joining rides and products to produce the combined conversion rate.
This question from PayPal's Technical 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
Index optimization and query performance
NULL handling and COALESCE
Pandas vectorized operations and groupby
Data cleaning and transformation
Common Table Expressions (CTEs)
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 slowly changing dimensions in this scenario?
- How would you validate the correctness of your query results?
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Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we need to analyze two tables: rides and orders. The rides table contains information about rides taken by users, while the orders table includes details about products purcha...
Approach
- Identify the Necessary Columns: From the
ridestable, we need user IDs and ride counts; from theorderstable, we need user IDs and order counts. - Join Tables: Use a LEFT JOIN to conn...
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