Clustered Index Explanation | Dataford Interview Questions

Explain what a clustered index is and when it helps query performance.

Use the provided PostgreSQL tables to write the representative date-range query discussed in your explanation. Address PostgreSQL's distinction between an index and one-time table clustering.

Output

Return customer_name, order_id, order_date, and amount.
Include only orders in January 2025 with a positive amount and a matching customer.
Sort by order_date ascending, then order_id ascending.

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
amount	NUMERIC(10,2)	Order amount

Your question is Clustered Index Explanation. Start with the requirements and the two tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem