Optimize a slow query on rides
Last updated: May 29, 2026
Quick Overview
A query on rides is running slowly. Identify the bottleneck and optimize it.
Jane Street
Data Manipulation (SQL/Python)
Data Scientist
Jane Street
May 29, 2026Data Scientist
Onsite
Data Manipulation (SQL/Python)
Easy
9
7
3,895 solved
A query on rides is running slowly. Identify the bottleneck and optimize it.
This question from Jane Street'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
- Write syntactically correct SQL with proper JOIN and WHERE clauses
- Use GROUP BY and aggregate functions appropriately
- Handle NULL values correctly in your queries
- Explain the query execution plan at a high level
Key Topics to Cover
NULL handling and COALESCE
Index optimization and query performance
Subqueries and correlated subqueries
JOIN types and when to use each
Data cleaning and transformation
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
- What would you do if this query needs to run every 5 minutes?
- How would you validate the correctness of your query results?
- Can you rewrite this without using subqueries?
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Practice SQL ProblemsSample Answer
Problem Understanding
We are dealing with a dataset of rides which likely includes details such as ride ID, driver ID, passenger ID, timestamps, and ride duration. The goal is to optimize a slow-running SQL query that retr...
Approach
- Identify the Current Query: Start by retrieving the existing SQL query that is running slowly.
- Analyze Execution Plan: Use
EXPLAINto understand how the current query is being execute...
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