Database Query Optimization | Dataford Interview Questions

How would you optimize a database query for a high-traffic Tesla service to reduce latency and improve throughput?

Using the provided Tesla service tables, write a PostgreSQL query that returns the requested operational summary for active requests opened on or after March 1, 2025.

Output

One row per service center and service type, including rows where the service type is NULL.
Columns: center_name, service_type, open_request_count, and oldest_opened_at.
Include only matching service centers and active requests with status open or in_progress.
Order by center_name ascending, then service_type ascending with NULL values last.

Schema

service_requests

Column	Type	Description
request_idPK	INT	Service request identifier
center_id	INT	Service center identifier
service_type	VARCHAR(80)	Requested service category
status	VARCHAR(30)	Current request status
opened_at	TIMESTAMP	Timestamp when the request was opened

service_centers

Column	Type	Description
center_idPK	INT	Service center identifier
center_name	VARCHAR(100)	Tesla service center name
city	VARCHAR(80)	City where the service center operates

Your question is Database Query Optimization. Start with the requirements and the two tables in the Question tab.

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Problem