Problem Statement

Problem Description You are working on a billing application and need to generate a report of customers along with a transcript of their transaction history. Write a query to aggregate the transactions for each customer. The query must calculate the total transaction amount and generate a formatted string of the chronological transaction history. 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 is separated by its mathematical sign surrounded by