Sales by Month and User | Dataford Interview Questions

Your question is Sales by Month and User. Start with the requirements and the two tables on the right.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem

Edmunds wants a monthly view of sales performance by user for the current month and the two preceding calendar months. Write a PostgreSQL query that produces one row for every Edmunds user in each of those three months, including users with no sales.

Requirements

Generate the three-month reporting window dynamically from CURRENT_DATE.
Aggregate sales amount, sales quantity, and transaction count by calendar month and user.
Show zero totals for users without sales in a month.
Use LAG to calculate the prior month's sales amount and sales change.
Rank users within each month by total sales amount, highest first, with user ID as a deterministic tie-breaker.
Return results ordered by month, rank, and user ID.

Schema

users

Column	Type	Description
user_idPK	INTEGER	Edmunds user identifier
user_name	VARCHAR(100)	User display name

sales

Column	Type	Description
sales_idPK	INTEGER	Unique sale identifier
user_id	INTEGER	User who made the sale
sales_date	DATE	Date the sale occurred
sales_amount	NUMERIC(12,2)	Sale amount, including refunds
sales_quantity	INTEGER	Number of units in the sale