SQL Orders Count Per Customer | Dataford Interview Questions

Your question is SQL Orders Count Per Customer. Start with the requirements and the two tables on the right.

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Problem

Dayforce needs a customer-level order count for a QA validation report. Write a PostgreSQL query that returns every customer and the total number of orders associated with that customer, including customers who have placed no orders.

Requirements

Use a LEFT JOIN from customers to orders so customers without orders remain in the result.
Count orders per customer using the order primary key, not COUNT(*), so unmatched customers receive a count of zero.
Return the customer name and an aliased column named order_count.
Sort the output alphabetically by customer name.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
created_at	DATE	Date the customer record was created

orders

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