Month-over-Month Sales SQL | Dataford Interview Questions

Business Context

Daimler Truck North America wants to monitor monthly truck sales performance across sales regions and identify regional increases or declines.

Write a PostgreSQL query that compares monthly truck sales by region from January through April 2024.

Join truck_sales to regions using region_id.
Aggregate sales by region and calendar month.
Use LAG to return the prior available month’s sales for each region.
Calculate the absolute and percentage month-over-month change. Return the results ordered by region and month. If there is no prior month or the prior value is zero, return NULL for percentage change.

regions

Column	Type	Description
region_idPK	INT	Unique sales region identifier
region_name	VARCHAR(50)	Daimler Truck sales region name

truck_sales

Column	Type	Description
sale_idPK	INT	Unique truck sale identifier
region_id	INT	Region associated with the sale
sale_date	DATE	Date on which the sale was recorded
sale_amount	NUMERIC(12,2)	Sale value in US dollars

Your question is Month-over-Month Sales SQL. Start with the requirements and the two tables in the Question tab.

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