title: SQL Join condition clause
body: <p>I have database with as diagram shows (see picture below)
  <a href="https://i.stack.imgur.com/z72a5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z72a5.png" alt="enter image description here"></a></p>
  
  <p>My task is to show total value of orders handled by each Employees.
  I have SQL statement:</p>
  
  <pre><code>SELECT e.FirstName,
         e.LastName,
         SUM(od.Quantity * od.UnitPrice * (1-od.Discount)) 
  FROM Orders AS o
  JOIN Employees AS e
  ON o.EmployeeID = e.EmployeeID
  JOIN [Order Details] AS od
  ON o.OrderID = od.OrderID
  GROUP BY e.FirstName,e.LastName
  </code></pre>
  
  <p>I have problem with further steps. I need to limited results only for those employees which:</p>
  
  <ul>
  <li>A) Have employees under them </li>
  <li>B) Don't have any employees under them</li>
  </ul>
  
  <p>I know It concern field ReportsTO in Employees table, but I don't know how get proper SQL clause. I am supposed to do with "EXISTS" or self-join ?</p>
  
  <p>Thank You.</p>