MathWorks·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

MathWorks software engineer interview with a SQL question that looked manageable on the surface but had enough moving parts to slow me down. The coupon validation logic and the LEAST() cap on discounts were where things got interesting.

Questions Asked (1)

Given an orders table and a coupons table, write a SQL query that computes the final cost per order, where the discount is the lesser of (subtotal * discount_pct) and max_discount, only applied when the coupon code matches and the order date falls within the coupon's validity window, and an 8% tax is applied on the discounted subtotal.

Data ModelingTechnical Trade-offs

Author's notes

The join itself was fine, a left join on coupon code plus a date range condition in the ON clause.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the schema and business rules, then build the query in stages: join orders to coupons on code and date validity, compute the discount as the minimum of percentage-based and capped amounts, and finally apply tax on the discounted subtotal. Use a LEFT JOIN to preserve orders without valid coupons and handle NULLs appropriately.

Pro tip: Mention that you would validate the query with edge cases like orders exactly on the coupon start/end date, coupons with no max_discount, and orders with no matching coupon, to ensure correctness and avoid silent data issues.

1. Clarify schema and rules

Confirm column names, data types, and business logic: coupon matching on code, date validity inclusive, discount calculation, and tax application. Ask about NULL handling and rounding.

2. Join orders with coupons

Use a LEFT JOIN on coupon code and order date between start_date and end_date to include all orders, even those without a valid coupon.

3. Compute discount

Calculate discount as LEAST(subtotal * discount_pct, max_discount) when coupon is valid; otherwise 0. Use COALESCE to handle NULLs from the LEFT JOIN.

4. Apply tax and final cost

Compute discounted subtotal as subtotal - discount, then final cost as discounted subtotal * 1.08. Round appropriately if needed.

5. Validate and optimize

Test with edge cases (boundary dates, no coupon, max_discount null) and consider indexing on coupon code and date ranges for performance.

Key Points to Mention

Use LEFT JOIN to preserve orders without valid coupons and COALESCE to default discount to 0.
Date validity should be inclusive: order_date BETWEEN start_date AND end_date.
Discount is LEAST(subtotal * discount_pct, max_discount) only when coupon matches and is valid.
Tax is applied on the discounted subtotal, not the original subtotal.
Handle NULL max_discount by treating it as unlimited or using a large number.
Consider rounding and data types (e.g., decimal vs float) for monetary calculations.

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