Write a query to find cumulative sum from users

Last updated: April 6, 2026

Quick Overview

Write a SQL query to calculate cumulative sum from the users table, considering nulls and duplicates.

SentinelOne

Data Manipulation (SQL/Python)

Data Scientist

SentinelOne

April 6, 2026

Data Scientist

Onsite

Data Manipulation (SQL/Python)

Hard

3,250 solved

Write a SQL query to calculate cumulative sum from the users table, considering nulls and duplicates.

SentinelOne asks this during the Onsite because data engineering skills are critical for the role. You should be comfortable with complex joins, window functions, CTEs, and performance optimization.

What the Interviewer Expects

Solve complex analytical problems with elegant, readable SQL
Optimize queries for large-scale datasets with partitioning and indexing
Use recursive CTEs, lateral joins, and advanced window functions
Design the data model alongside the query solution
Discuss trade-offs between SQL and programmatic approaches (Python/pandas)
Consider the operational aspects: query scheduling, incremental processing

Key Topics to Cover

Aggregate functions and GROUP BY

Pandas vectorized operations and groupby

JOIN types and when to use each

Index optimization and query performance

Subqueries and correlated subqueries

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

How would you optimize this query for a table with 100 million rows?
How would you handle slowly changing dimensions in this scenario?
Can you rewrite this without using subqueries?
What indexes would you create to support this query?

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Practice SQL Problems

Sample Answer

Problem Understanding

The task is to calculate a cumulative sum from the users table. This table may contain user-specific data, including fields such as user ID, login times, or any metric we want to sum. The cumulative...

Approach

Identify Columns: Determine which column(s) in the users table will be used for the cumulative sum. For instance, if we are summing a login_count column, we need to ensure that we account f...

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