Sales by Month and User | Dataford Interview Questions

Edmunds wants a monthly view of sales performance by user for June through August 2026. Write a PostgreSQL query that produces one row for every Edmunds user in each of those three months, including users with no sales.

Output

One row per user and reporting month, for June, July, and August 2026.
Columns: sales_month, user_id, user_name, total_sales, total_quantity, sales_count, previous_month_sales, sales_change, and sales_rank.
Missing sales amounts and quantities contribute zero to monthly totals. A sale with a NULL amount still counts as a sale, but contributes zero to total_sales.
The previous-month value is NULL for June. Users are ranked within each month by total sales descending, with tied totals sharing a rank.
Order 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

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