Fidelity·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

SQL-heavy technical screen for a software engineer role at Fidelity. The main focus was a classic ranking problem but they pushed pretty hard on edge cases and generalizing the solution, which I wasn't fully prepared for.

Questions Asked (1)

Given an Employee table with id and salary columns, write a SQL query to return the third highest distinct salary. If fewer than three distinct salaries exist, return NULL. Be prepared to discuss multiple approaches and generalize to the Nth highest.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

Started with the DENSE_RANK() approach because it felt cleanest, wrapping it in a CTE and filtering where rank = 3.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: return the third highest distinct salary, or NULL if fewer than three distinct salaries exist. Then present at least two SQL approaches—using window functions (DENSE_RANK) and a correlated subquery with LIMIT/OFFSET—and discuss their trade-offs. Finally, generalize to the Nth highest salary and mention edge cases like duplicates and NULL handling.

Pro tip: Demonstrate awareness of performance: DENSE_RANK with an index on salary is efficient for large datasets, while LIMIT/OFFSET can be slower for high N. Also, explicitly handle the NULL case using a subquery or COALESCE to show attention to detail.

1. Clarify requirements and edge cases

Confirm that 'third highest distinct salary' means the third unique salary value when sorted descending, and that NULL should be returned if fewer than three distinct salaries exist. Ask about NULL salaries and whether ties should be considered.

2. Present a window function approach

Use DENSE_RANK() OVER (ORDER BY salary DESC) to assign ranks to distinct salaries, then select the salary where rank = 3. Wrap in a subquery or CTE and use a scalar subquery to return NULL if no such rank exists.

3. Present an alternative approach

Use a correlated subquery with LIMIT/OFFSET: SELECT DISTINCT salary FROM Employee ORDER BY salary DESC LIMIT 1 OFFSET 2. Explain that this returns NULL automatically if fewer than three rows, but may be less efficient for large offsets.

4. Generalize to Nth highest

Show how to parameterize the query for any N: replace the rank condition with rank = N, or use LIMIT 1 OFFSET N-1. Discuss that DENSE_RANK handles duplicates correctly, while LIMIT/OFFSET requires DISTINCT.

5. Discuss trade-offs and performance

Compare the approaches: window functions are more flexible and often faster for large N, but may require sorting; LIMIT/OFFSET is simple but can be slow for high offsets. Mention indexing on salary to improve performance.

Key Points to Mention

Use of DENSE_RANK() to handle duplicate salaries correctly
Correlated subquery with LIMIT/OFFSET as an alternative
Handling the NULL case when fewer than N distinct salaries exist
Generalization to Nth highest salary (parameterization)
Performance considerations: indexing, sorting, and offset efficiency
Edge cases: NULL salaries, ties, and negative salaries

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