Calculate retention rate per user from transactions
Last updated: July 6, 2025
Quick Overview
Write SQL to compute retention rate grouped by user from transactions, handling nulls and duplicates.
Walmart
Data Manipulation (SQL/Python)
Data Scientist
Walmart
July 6, 2025Data Scientist
Phone Screen
Data Manipulation (SQL/Python)
Easy
541
8
1,955 solved
Write SQL to compute retention rate grouped by user from transactions, handling nulls and duplicates.
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
The goal is to calculate the retention rate per user based on transaction data from Walmart. The retention rate typically refers to the percentage of users who continue to make purchases over time. In...
Approach
- Identify Unique Users: Start by selecting distinct user IDs from the transactions table.
- Count Transactions: For each user, count the number of transactions they made within a specifie...
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