Optimizing a Slow SQL Query | Dataford Interview Questions

How would you optimize a slow-running query in SQL?

Using the provided PostgreSQL tables, return customers whose completed orders total at least 1,000 during the first quarter of 2025. Rows with a NULL status, order date, amount, or customer reference are ignored.

Output

One row per qualifying customer with customer_id, customer_name, total_spend, and completed_orders.
Sort by total_spend descending, then customer_id ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
region	VARCHAR(50)	Customer region

orders

Column	Type	Description
order_idPK	INT	Unique order identifier
customer_id	INT	Customer associated with the order
order_date	DATE	Order placement date
status	VARCHAR(20)	Order processing status
amount	NUMERIC(12,2)	Order amount

Your question is Optimizing a Slow SQL Query. Start with the requirements and the two tables in the Question tab.

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Problem