Optimize a Slow SQL Query in Azure | Dataford Interview Questions

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

Asked in the technical interview stage. Azure Data Engineer, 4-5 yrs exp.

For grading, use customers, orders, order_items, and products. Return completed orders from the first quarter of 2025 for products in the Home Care category, including only customers whose category spend exceeds 100.

Output

One row per qualifying customer.
Columns: customer_id, customer_name, order_count, and total_spend.
Include only completed orders dated from 2025-01-01 through 2025-03-31.
Sort by total_spend descending, then customer_id ascending.

Schema

customers

Column	Type	Description
customer_idPK	INT	Customer identifier
customer_name	VARCHAR(100)	Customer display name
region	VARCHAR(50)	Customer region
status	VARCHAR(20)	Customer account status

orders

Column	Type	Description
order_idPK	INT	Order identifier
customer_id	INT	Customer who placed the order
order_date	DATE	Date the order was placed
order_status	VARCHAR(20)	Order processing status

order_items

Column	Type	Description
order_item_idPK	INT	Order line identifier
order_id	INT	Referenced order
product_id	INT	Referenced product
quantity	INT	Units purchased
unit_price	NUMERIC(10,2)	Price per unit

products

Column	Type	Description
product_idPK	INT	Product identifier
product_name	VARCHAR(100)	Product name
category	VARCHAR(50)	Product category

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Problem