Meta·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Meta data/analytics interview, one SQL-heavy question that sounds straightforward until you actually try to write it out. The join logic for detecting active rentals on a specific date is the part that trips people up.

Questions Asked (1)

Given a rentals table with start and end dates and a cars table with location and size info, write a query to find, as of a specific date, how many cars are currently rented out per city and car size, the total stock for each city/car size combination, and the ratio of rented to total stock.

Data ModelingProduct Analytics & MetricsSystem Design

Author's notes

The ratio part is almost decorative, it's just a division at the end.

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AI HintsAI Generated

Suggested Approach

Clarify the schema and the meaning of 'currently rented out' (e.g., start_date <= target_date AND end_date > target_date). Then write a query that joins rentals to cars, filters active rentals, and aggregates counts per city and size, while separately computing total stock from the cars table. Finally, combine these using a LEFT JOIN or subqueries to compute the ratio.

Pro tip: Mention that you would handle cities or sizes with zero rentals by using a LEFT JOIN and COALESCE to avoid division by zero, and that you'd consider indexing on (start_date, end_date) for performance.

1. Clarify requirements and schema

Ask about the exact columns, data types, and whether 'currently rented out' means the rental period includes the target date (start <= date < end). Confirm if cars can be rented from different locations than their home location.

2. Compute total stock per city and size

Write a subquery that groups the cars table by city and size, counting the number of cars. This gives the denominator for the ratio.

3. Compute rented cars per city and size as of the date

Write a subquery that joins rentals to cars, filters for active rentals (start_date <= target_date AND end_date > target_date), and groups by city and size, counting distinct rentals or cars.

4. Combine results and calculate ratio

Use a LEFT JOIN from total stock to rented counts (or FULL OUTER JOIN) to ensure all city/size combos appear. Compute ratio as rented / total, handling division by zero with NULLIF or CASE.

5. Optimize and discuss edge cases

Mention indexing on rental dates and car location/size, and discuss how to handle cars with no rentals, multiple rentals overlapping, or missing data.

Key Points to Mention

Definition of 'currently rented out': start_date <= target_date AND end_date > target_date (or >= depending on inclusivity).
Use of LEFT JOIN to include city/size combinations with zero rentals.
Handling division by zero with NULLIF or CASE WHEN total > 0.
Indexing on rentals(start_date, end_date) and cars(city, size) for performance.
Potential need to count distinct cars if a car can have multiple rentals overlapping (though typically not).
Consideration of time zones and date boundaries if applicable.

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