title: SQL add relations to relation table
body: <p>I have 3 tables which manage the users an their rights</p>
  
  <pre><code>Employee
  +-----------+------+
  |EmployeeID | Name |
  +-----------+------+
  |1          |Tim   |
  |2          |Tom   |
  +-----------+------+
  
  Right
  +-----------+------+
  |RightID    |Name  |
  +-----------+------+
  |1          |Read  |
  |2          |Write |
  |3          |Change|
  +-----------+------+
  
  EmployeeRight
  +-----------+--------+
  |EmplyeeID  | RightID|
  +-----------+--------+
  |1          |1       |
  |1          |2       |
  |2          |1       |
  +-----------+--------+
  </code></pre>
  
  <p>Now I need to give all users the right "Change" which have the right "Write". But users that already have that right should not get it twice.</p>
  
  <p>My current attempt does not work:</p>
  
  <pre><code>INSERT INTO EmployeeRight 
  (SELECT '3', EmployeeID FROM EmployeeRight WHERE RightID = 2 AND RightID !=3)
  </code></pre>