Optimize a Slow Query | Dataford Interview Questions

Discuss how you would optimize a slow-running query.

Assume the query joins Booking properties, cities, and bookings to count distinct guests for properties in the Netherlands during the first quarter of 2025. Explain the optimization approach and provide the resulting query for the required output.

Output

One row per Netherlands property, including properties with no qualifying bookings.
Columns: property_id, property_name, city_name, and unique_guests.
Include only bookings from 2025-01-01 through 2025-03-31, order by unique_guests descending, then property_id ascending.

Schema

properties

Column	Type	Description
property_idPK	INT	Unique property identifier
property_name	VARCHAR(120)	Displayed property name
city_id	INT	Referenced city identifier

cities

Column	Type	Description
city_idPK	INT	Unique city identifier
city_name	VARCHAR(100)	City name
country_code	CHAR(2)	ISO country code

bookings

Column	Type	Description
booking_idPK	INT	Unique booking identifier
property_id	INT	Booked property identifier
guest_id	INT	Guest identifier
check_in_date	DATE	Scheduled check-in date

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Problem