I was reading this document here and I am stuck on what the E, S, are referring to in the line
100 * Salary::Salary / ExecuteSQL("select sum(S.salary) from Employees E join Salary S on E.EmpID = S.EmpID where E.Department = ?"; ""; ""; Department)
If S and E are abbreviations for the Employees and Salaries table when was that defined? Or does it just go without saying? Why is the E after Employees at one part of the statement?