TikTok·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

TikTok data scientist SQL round, one question but with enough follow-ups to keep you on your toes for a while. Pretty standard window function territory but the edge case discussion got interesting.

Questions Asked (1)

Write a SQL query to return the top 1 highest-paid employee per department, given a table that may have multiple rows per employee per department due to historical salary changes.

Data ModelingTechnical Trade-offsProduct Analytics & Metrics

Author's notes

My first instinct was ROW_NUMBER() partitioned by department, ordered by salary descending, which is correct.

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AI HintsAI Generated

Suggested Approach

First, clarify the table schema and whether 'highest-paid' refers to current or historical salary. Then, use a window function like ROW_NUMBER() partitioned by department and ordered by salary descending to rank employees, and filter to the top rank per department. Handle ties appropriately based on business rules.

Pro tip: Mention that you would confirm with stakeholders whether to include only current employees or all historical records, and whether ties should return multiple employees or just one. This shows you think about data semantics and business context, not just syntax.

1. Clarify requirements and schema

Ask about the table structure, what 'highest-paid' means (e.g., current salary vs. historical max), and how to handle ties. Confirm if the output should include department, employee, and salary.

2. Choose the right window function

Use ROW_NUMBER() or RANK()/DENSE_RANK() depending on tie handling. ROW_NUMBER() gives exactly one row per department; RANK() allows ties. Partition by department and order by salary descending.

3. Write the query with a subquery or CTE

Create a subquery or CTE that computes the rank for each employee within each department. Then filter to rank = 1 in the outer query.

4. Consider performance and edge cases

Mention indexing on department and salary, and how the query scales. Discuss handling of NULL salaries, departments with no employees, and duplicate rows due to historical changes.

5. Validate and explain results

Run the query on sample data, check for correctness, and explain how the output answers the business question. Be ready to discuss alternative approaches like correlated subqueries or GROUP BY with MAX.

Key Points to Mention

Use of window functions (ROW_NUMBER, RANK, DENSE_RANK) for top-N per group
Partitioning by department and ordering by salary descending
Handling ties: ROW_NUMBER vs RANK vs DENSE_RANK
Filtering with a subquery or CTE to get rank = 1
Performance considerations: indexing, data volume, and query execution plan
Business context: current vs historical salary, and whether to include all employees or only active ones

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.