title: "ALTER ROLE db_owner ADD MEMBER A" doesn't work
body: <p>When I execute <code>ALTER ROLE db_owner ADD MEMBER A</code> it gives out following error.</p>
  
  <blockquote>
    <p>Msg 15151, Level 16, State 1, Line 4<br>
    Cannot alter the role 'A', because it does not exist or you do not have permission.</p>
  </blockquote>
  
  <p>Here <a href="https://msdn.microsoft.com/en-us/library/ms189775.aspx" rel="noreferrer">ALTER ROLE</a> it mentions that;</p>
  
  <blockquote>
    <p>Limitations and restrictions</p>
    
    <p>You cannot change the name of a fixed database role.</p>
  </blockquote>
  
  <p>But I can't find any relationship to this with the error. What I'm trying to do is adding a  member not changing the fixed role name.</p>
  
  <p>Any support in resolving this matter is highly appreciated</p>