Write a query to display the employee number, last name, first name, and sum of invoice totals for all employees who completed an invoice. Sort the output by employee last name and then by first name. (Hint: you are working with two tables, EMPLOYEE and INVOICE. The tables are linked using the foreign key INVOICE_NO present in the EMPLOYEE table, and is also the primary key of the INVOICE table. Assume any other attributes or tables you may require to generate the sum of invoice. Do clearly state your assumptions).