Detect Subscription Price Increases | Dataford Interview Questions

Given a table of user transactions, identify all recurring subscription payments that increased in price compared to the previous month at Truebill.

Consider only transactions marked as recurring. A payment qualifies only when the same subscription has a payment in the immediately preceding calendar month.

Output

One row per qualifying subscription payment.
Return user_name, merchant_name, payment_month, current_amount, and previous_amount.
Sort by payment_month, then user_name, then subscription_id.

Schema

users

Column	Type	Description
user_idPK	INT	Unique Truebill user identifier
user_name	VARCHAR(100)	Display name of the user

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
subscription_id	INT	Identifier for the recurring subscription
user_id	INT	User associated with the transaction
merchant_name	VARCHAR(100)	Subscription merchant name
payment_date	DATE	Date the payment was made
amount	DECIMAL(10,2)	Payment amount in dollars
is_recurring	BOOLEAN	Whether the transaction is classified as recurring

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Problem