Partitioning and Query Performance | Dataford Interview Questions

Explain the concept of data partitioning and how it impacts query performance.

Demonstrate the explanation with a PostgreSQL query that retrieves project costs for the first quarter of 2025. The date predicate should allow a range-partitioned cost table to exclude irrelevant partitions.

Output

One row per office included in the filtered data
Columns: office_name, total_cost
Include only costs from January 1 through March 31, 2025
Order by total_cost descending, then office_name ascending with null office names last

Schema

project_costs

Column	Type	Description
cost_idPK	INT	Unique cost record identifier
office_id	INT	Office associated with the cost
cost_date	DATE	Cost date and range-partitioning key
amount	DECIMAL(12,2)	Recorded project cost

offices

Column	Type	Description
office_idPK	INT	Unique office identifier
office_name	VARCHAR(100)	Display name of the office
region	VARCHAR(50)	Geographic region

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Problem