Nested selects

SELECT FirstName, LastName, Salary
FROM Employees
WHERE Salary =
  (SELECT MAX(Salary) FROM Employees)

---------------------------------------------------------------------

SELECT FirstName, LastName, DepartmentID, Salary
FROM Employees
WHERE DepartmentID IN
  (SELECT DepartmentID FROM Departments
   WHERE Name='Sales')

---------------------------------------------------------------------

SELECT FirstName, LastName, DepartmentID, Salary
FROM Employees e
WHERE Salary =
  (SELECT MAX(Salary) FROM Employees
   WHERE DepartmentID = e.DepartmentID)
ORDER BY DepartmentID

---------------------------------------------------------------------

SELECT FirstName, LastName, EmployeeID, ManagerID
FROM Employees e
WHERE EXISTS
  (SELECT EmployeeID
   FROM Employees m
   WHERE m.EmployeeID = e.ManagerID
     AND m.DepartmentID = 1)