Optimizing Slow SQL Queries | Dataford Interview Questions

How do you optimize a slow SQL query?

Review the query represented by the supplied tables and produce an efficient PostgreSQL query that returns only qualifying active customers. The result must calculate completed 2025 order revenue and exclude customers whose total is not greater than 1,000.

Output

One row per qualifying active customer.
Columns: customer_id, customer_name, total_completed_revenue.
Include only completed orders from 2025 and totals greater than 1,000.
Sort by total revenue descending, then customer name ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Unique customer identifier
customer_name	VARCHAR(100)	Customer display name
status	VARCHAR(20)	Customer lifecycle status

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
amount	DECIMAL(12,2)	Order value
status	VARCHAR(20)	Order processing status

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