Window function: rank over sessions
Last updated: October 15, 2025
Quick Overview
Use window functions to compute rank partitioned by user_id over sessions.
Walmart
Data Manipulation (SQL/Python)
Data Scientist
Walmart
October 15, 2025Data Scientist
Technical Screen
Data Manipulation (SQL/Python)
Medium
685
15
2,515 solved
Use window functions to compute rank partitioned by user_id over sessions.
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.
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Practice SQL ProblemsSample Answer
Problem Understanding
In this problem, we are tasked with analyzing user sessions data to compute a ranking of sessions for each user. The data involved likely includes fields such as user_id, session_id, `session_star...
Approach
- Identify the relevant columns from the session data:
user_id,session_id, and potentially a metric for ranking such assession_start_timeorduration. - Use a window function to rank the s...
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