Intermediate SQL Questions | Dataford Interview Questions

Answer three intermediate SQL questions.

Write PostgreSQL queries for the three requirements below using the provided tables. Treat only orders with status = 'completed' as completed transactions. Preserve customers with no completed orders where requested.

Output

Return each customer’s completed order count and total completed amount.
Return monthly completed order count and revenue for 2025, including months with completed orders only.
Return customers with at least two completed orders, their total amount, and their rank by total amount. Sort each result as specified.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name

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
status	VARCHAR(20)	Order status
amount	DECIMAL(10,2)	Order amount

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Problem