Weekly Active Purchaser Growth Rate | Dataford Interview Questions

Your question is Weekly Active Purchaser Growth Rate. Start with the requirements and the two tables on the right.

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Problem

ShopWave wants to track how its active purchaser base changes week over week. Write a PostgreSQL query to calculate the weekly count of active purchasers and the week-over-week growth rate.

An active purchaser is a user who has at least one completed transaction in a given calendar week. Use the transaction date to assign each purchase to a week.

Requirements

Count distinct purchasers per week using only transactions with status = 'completed'.
Return one row per week, even if there are zero active purchasers that week.
Calculate the prior week's active purchaser count.
Compute week-over-week growth rate as: ((current_week_active_purchasers - previous_week_active_purchasers) / previous_week_active_purchasers) * 100 Return NULL when the previous week is 0 or missing.
Order the output by week start date ascending.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
user_id	INT	User who made the transaction
transaction_date	DATE	Date the transaction occurred
amount	DECIMAL(10,2)	Transaction amount
status	VARCHAR(20)	Transaction processing status
store_id	INT	Store identifier

users

Column	Type	Description
user_idPK	INT	Unique user identifier
user_name	VARCHAR(100)	User full name
signup_date	DATE	Date the user signed up
country	VARCHAR(50)	User country