Revenue by Month From Orders | Dataford Interview Questions

Mutual of Omaha's customer portal reporting team needs a monthly revenue summary based only on orders associated with known customers. Write a PostgreSQL query that joins orders to customers and aggregates order amounts by calendar month.

Requirements

Join each order to its matching customer using customer_id.
Exclude orders without a matching customer or a valid order_date.
Return the month as YYYY-MM and total revenue for that month, ignoring NULL amounts.
Sort the results chronologically by month.

Schema

customers

Column	Type	Description
customer_idPK	INTEGER	Unique customer identifier
customer_name	VARCHAR(100)	Customer's full name
email	VARCHAR(150)	Customer email address

orders

Column	Type	Description
order_idPK	INTEGER	Unique order identifier
customer_id	INTEGER	References customers.customer_id
order_date	DATE	Date the order was placed
order_amount	NUMERIC(12,2)	Revenue amount for the order

Your question is Revenue by Month From Orders. Start with the requirements and the two tables in the Question tab.

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