Capital One·Data Scientist·Technical Phone Screen·Intermediate

Intermediate

Jul 2026

Summary

Capital One data scientist interview with a SQL-heavy technical screen. One question but it was a real one, not the usual 'write a basic join' stuff they sometimes throw out.

Questions Asked (1)

Given a products table and a purchases table, return the minimum purchase price per category where at least one purchase has a star rating above 4. Categories with no qualifying purchases should return 0, not NULL. Output one row per category sorted alphabetically.

Data ModelingProduct Analytics & Metrics

Author's notes

This one took me longer than it should have.

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AI HintsAI Generated

Suggested Approach

Start by identifying categories that have at least one purchase with a star rating above 4 using a subquery or join. Then compute the minimum purchase price per qualifying category, and finally left join back to all categories to fill missing values with 0, ensuring the output is sorted alphabetically.

Pro tip: Always clarify how to handle ties or missing data, and explicitly mention that you're using a LEFT JOIN with COALESCE to replace NULLs with 0, as this shows attention to data completeness and business requirements.

1. Identify qualifying categories

Filter purchases to those with star rating > 4, then extract distinct category IDs from the products table.

2. Compute minimum price per category

For each qualifying category, calculate the minimum purchase price from the purchases table.

3. Include all categories

Left join the aggregated results to the full list of categories to ensure categories without qualifying purchases are included.

4. Replace NULLs with 0

Use COALESCE or IFNULL to convert NULL minimum prices to 0 for categories with no qualifying purchases.

5. Sort and output

Order the final result alphabetically by category name and select the required columns.

Key Points to Mention

Use of LEFT JOIN to retain all categories, including those without qualifying purchases.
Application of COALESCE (or equivalent) to replace NULL with 0.
Filtering condition: star_rating > 4 (strictly greater than).
Aggregation with MIN() to get the minimum purchase price per category.
Sorting the final output alphabetically by category.
Handling of potential duplicates or multiple purchases per product.

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