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Instacart·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Bizops interview at Instacart with a SQL-heavy analytical question focused on driver efficiency. Pretty straightforward setup but the metric definition was the tricky part.

Questions Asked (1)

Q1

Write a SQL query to find the least efficient driver based on deliveries completed per hour of driving time over the last two months.

Product Analytics & MetricsData Modeling
Author's notes

The SQL itself wasn't the hard part.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the metric definition: deliveries per hour of driving time, and the time window of the last two months. Then outline a query that aggregates deliveries and driving hours per driver, computes the ratio, and selects the driver with the lowest ratio, handling edge cases like zero driving hours.

Pro tip: Mention that you would exclude drivers with very few deliveries or driving hours to avoid misleading ratios from small sample sizes, and consider using a HAVING clause to filter them out.

1. Clarify the metric and requirements

Confirm that 'least efficient' means the lowest deliveries per hour of driving time, and that the time window is the last two months from the current date. Ask about data sources and any filters (e.g., active drivers only).

2. Identify relevant tables and columns

Assume tables like deliveries (driver_id, delivery_id, completed_at) and driver_shifts (driver_id, shift_start, shift_end, driving_hours) or similar. Determine how to calculate driving hours per driver.

3. Aggregate deliveries and driving hours per driver

Write subqueries or CTEs to count completed deliveries and sum driving hours for each driver within the last two months. Ensure you filter by date and handle any NULLs.

4. Compute efficiency ratio and select least efficient

Join the aggregated results, calculate deliveries / driving_hours, and order ascending to get the lowest ratio. Use LIMIT 1 to return the least efficient driver.

5. Handle edge cases and validate

Exclude drivers with zero driving hours or very few deliveries to avoid division by zero or skewed results. Consider adding a minimum threshold for deliveries or hours.

Key Points to Mention

  • Definition of efficiency: deliveries completed divided by total driving hours.
  • Time window: last two months, using a date filter like completed_at >= DATE_SUB(CURRENT_DATE, INTERVAL 2 MONTH).
  • Aggregation: use COUNT for deliveries and SUM for driving hours, grouped by driver_id.
  • Join between deliveries and driving hours data, possibly from different tables.
  • Handling division by zero: use NULLIF or filter out drivers with zero driving hours.
  • Ordering and limiting: ORDER BY efficiency ASC LIMIT 1 to find the least efficient driver.

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