Amazon·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

SQL technical screen for a Data Scientist role at Amazon. One question, focused on window functions and salary ranking per department. Pretty standard stuff if you've done this kind of analysis before.

Questions Asked (1)

Given an employees table with salary and department columns, write a SQL query that returns the top 3 distinct salary amounts within each department.

Data ModelingTechnical Trade-offs

Author's notes

I went straight for DENSE_RANK which felt right since ties shouldn't eat up a rank slot.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: 'top 3 distinct salary amounts' means we need to rank distinct salaries per department and filter to the top 3. Use a window function like DENSE_RANK() partitioned by department and ordered by salary descending, then filter where rank <= 3. This handles ties correctly and ensures distinct salaries.

Pro tip: Mention that DENSE_RANK() is preferred over ROW_NUMBER() or RANK() because it correctly handles duplicate salaries and ensures exactly the top 3 distinct amounts. Also, note that if the table is large, partitioning by department and ordering by salary can be optimized with an index on (department, salary).

1. Clarify requirements

Confirm that 'top 3 distinct salary amounts' means the three highest unique salary values per department, and that ties should not reduce the number of distinct salaries returned.

2. Choose ranking function

Select DENSE_RANK() as the window function because it assigns the same rank to identical salaries and does not skip ranks, ensuring we get exactly the top 3 distinct values.

3. Write the window function query

Construct a subquery or CTE that computes DENSE_RANK() OVER (PARTITION BY department ORDER BY salary DESC) as salary_rank, selecting department and salary.

4. Filter and format output

In the outer query, filter WHERE salary_rank <= 3 and select department and salary, optionally ordering by department and salary descending for readability.

5. Discuss trade-offs and performance

Explain why DENSE_RANK() is better than alternatives (e.g., ROW_NUMBER() would not handle ties, RANK() would skip ranks) and mention indexing strategies for large datasets.

Key Points to Mention

Use of DENSE_RANK() to handle duplicate salaries and ensure distinct values.
Partitioning by department and ordering by salary descending.
Filtering with a subquery or CTE to apply the rank condition.
Comparison with ROW_NUMBER() and RANK() and why DENSE_RANK() is appropriate.
Performance considerations: indexing on (department, salary) and potential use of QUALIFY in some databases.
Edge cases: departments with fewer than 3 distinct salaries, NULL salaries, and how they are handled.

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