Window function: rank over category
Last updated: June 11, 2026
Quick Overview
Use window functions to compute running total partitioned by user_id.
Salesforce
Data Manipulation (SQL/Python)
Data Scientist
Salesforce
June 11, 2026Data Scientist
Onsite
Data Manipulation (SQL/Python)
Easy
49
5
3,359 solved
Use window functions to compute running total partitioned by user_id.
Data manipulation questions at Salesforce test your ability to work with real-world datasets. This Onsite question evaluates your SQL proficiency, understanding of data modeling, and ability to derive insights from raw data.
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
Index optimization and query performance
Data cleaning and transformation
Window functions (ROW_NUMBER, RANK, LAG, LEAD)
Date/time manipulation
JOIN types and when to use each
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 indexes would you create to support this query?
- Can you rewrite this without using subqueries?
- How would you handle slowly changing dimensions in this scenario?
Sharpen Your Skills on Codemia
Practice similar problems with our interactive workspace, get AI feedback, and track your progress.
Practice SQL ProblemsSample Answer
Problem Understanding
The task is to compute a running total for users, partitioned by user_id. We need to work with a dataset that contains at least two columns: user_id and amount (representing some numeric value t...
Approach
- Identify the Base Table: Start with the table that contains the
user_id,amount, and atimestampordatecolumn to order the records. - Use Window Function: To calculate the runni...
Submit Your Answer
Markdown supported