Window Function for Rent Growth | Dataford Interview Questions

Write a window function to calculate the month-over-month rent growth for our portfolio across different zip codes.

Use the properties and rent_observations tables. Calculate each ZIP code's average monthly rent and its percentage change from the previous reported month. Exclude the first month for each ZIP code because it has no prior comparison.

Output

One row per ZIP code and month with a prior reported month
Columns: zip_code, month_start, average_rent, and rent_growth_pct
Sort by zip_code, then month_start ascending

Schema

properties

Column	Type	Description
property_idPK	INT	Unique property identifier
property_name	VARCHAR(100)	Property name
zip_code	VARCHAR(5)	Property ZIP code

rent_observations

Column	Type	Description
observation_idPK	INT	Unique rent observation identifier
property_id	INT	Property associated with the observation
observed_on	DATE	Date of the rent observation
monthly_rent	NUMERIC(10,2)	Observed monthly rent amount

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