List the full name of all employees who work in the Northern region.
full names = FirstName, LastName; Northern region refers to RegionDescription = 'Northern';
SELECT DISTINCT T1.FirstName, T1.LastName FROM Employees AS T1 INNER JOIN EmployeeTerritories AS T2 ON T1.EmployeeID = T2.EmployeeID INNER JOIN Territories AS T3 ON T2.TerritoryID = T3.TerritoryID INNER JOIN Region AS T4 ON T3.RegionID = T4.RegionID WHERE T4.RegionDescription = 'Northern'