Problems with fetching fields from the database?

Question

SQL

For the depicted database schema, you need to create a query that will return a list of all accounts. For each account, select the fields Account Number, Account Date, Customer Name, and Customer Name referred to by the current account customer.
Let's say a query on the first 3 fields, I would do like this:

SELECT Invoices.Id, Customers.CBilling_date, Customers.Name
  FROM Invoices JOIN Customers ON (Customers.Id = Invoices.Customer_ID) 
  GROUP BY Invoices.Billing_date

But I don’t understand how to select the name of the client referred to by the client of the current account. After all, there is no such field at all in any table.

Answer 1

SELECT I.Id, 
       C.CBilling_date, 
       C.Name, 
       C2.Name -- Имя клиента, на которого ссылается клиент текущего счета
  FROM Invoices I 
       left join Customers C ON C.Id = I.Customer_ID
       left join Customers C2 ON C2.Id = C.Referred_ID

GROUP BY I.Billing_date