Problem Statement

Problem Description You are building reporting features for a billing platform, and one requirement is to show each customer alongside a readable transcript of everything that happened in their account. Write a query that rolls up each customer's transactions: it must compute the running total transaction amount and build a formatted string showing the transaction history in chronological order. Schema customers table: id : SMALLINT (Customer ID) iban : VARCHAR(255) (Client's IBAN number) transactions table: customer_id : SMALLINT (Foreign key to customers.id ) dt : VARCHAR(19) (Transaction timestamp in YYYY-MM-DD HH:MM:SS format) amount : DECIMAL(5,2) (Transaction amount, positive or negative) Required Output The result should contain the following columns: iban : The client's IBAN. transactions : A chronological string of transaction amounts (sorted by dt ascending) formatted as follows: The first amount is displayed exactly as it is (e.g., 31.14 or -20.25 ). Each subsequent amount i