Point72·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Point72 Data Scientist interview with a SQL-heavy technical screen. One meaty query question that covered window functions, nulls, and tie-breaking logic all at once. Felt like a real test of whether you actually know SQL or just know the basics.

Questions Asked (1)

Given a Departments table and a Students table (with nullable dept_id, nullable GPA, and an enrollment date), write a single SQL query that returns every department including ones with no students, along with their top student by GPA. Ties should break by earliest enrollment date, then by smallest student ID. If a department has no students with a non-null GPA, return that department row with nulls for all student fields.

Data ModelingAlgorithms & Data StructuresTechnical Trade-offs

Author's notes

This one took me a minute to untangle.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the schema and edge cases (nullable dept_id, GPA, ties). Then outline a solution using a LEFT JOIN from Departments to a ranked subquery of Students, where ranking uses ROW_NUMBER() with ORDER BY GPA DESC, enrollment_date ASC, student_id ASC. Finally, discuss performance considerations and alternative approaches like correlated subqueries or window functions with PARTITION BY.

Pro tip: Explicitly handle the case where a department has students but none have a non-null GPA: the ranking should still assign row numbers, but the join should filter to only the top-ranked student with non-null GPA, or use a conditional to return nulls. Mention that NULLs in GPA are excluded from ranking but departments with only null-GPA students must still appear with null student fields.

1. Clarify requirements and edge cases

Confirm that 'top student by GPA' means highest GPA, ties broken by earliest enrollment date then smallest student ID. Note that departments with no students or only students with null GPA should return null student fields.

2. Design the ranking logic

Use ROW_NUMBER() OVER (PARTITION BY dept_id ORDER BY GPA DESC, enrollment_date ASC, student_id ASC) to rank students within each department, ensuring null GPAs are handled (e.g., they will sort last or be excluded).

3. Join departments with ranked students

LEFT JOIN Departments to the ranked subquery on dept_id, filtering to only the top-ranked student (row_number = 1) or using a conditional to include departments with no qualifying students.

4. Handle nulls and finalize output

Ensure that for departments with no students or no non-null GPA students, the student columns are null. This may require a COALESCE or a CASE expression, or relying on the LEFT JOIN naturally producing nulls.

5. Discuss performance and alternatives

Mention indexing on dept_id and GPA, and compare window function approach to correlated subqueries or OUTER APPLY (if supported). Note trade-offs in readability and performance.

Key Points to Mention

Use of LEFT JOIN to include departments with no students.
Window function ROW_NUMBER() with PARTITION BY dept_id and ORDER BY GPA DESC, enrollment_date ASC, student_id ASC.
Handling of NULL GPA: either exclude from ranking or ensure they don't become the top student.
Tie-breaking logic: earliest enrollment date, then smallest student ID.
Ensuring departments with no qualifying students return null student fields.
Performance considerations: indexing, avoiding unnecessary sorting, and alternative approaches like correlated subqueries.

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