SQL: Customers With Multiple Orders | Dataford Interview Questions

The Cimpress Technology ordering platform needs to identify VistaPrint customers who placed multiple orders during the same calendar month. Write a PostgreSQL query that returns each qualifying customer, the month, and the number of orders placed during that month.

Requirements

Join customers to orders using customer_id.
Group orders by customer and calendar month, ignoring orders with a NULL order date.
Return only customer-month groups with more than one order.
Sort the output by customer_id and month ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(120)	Customer display name

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer who placed the order
order_date	DATE	Date the order was placed

Your question is SQL: Customers With Multiple Orders. Start with the requirements and the two tables in the Question tab.

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Problem