title: Modify primary key without dropping
body: <p>I have the following schema:</p>
  
  <blockquote>
    <p>Table T1 (c1 int (10), c2 int (10), c3 int (10), primary key(c1, c2))</p>
    
    <p>Table T2 (c1 int(10), c2 int (10), foreign key(c1, c2) references
    T1(c1,  c2));</p>
  </blockquote>
  
  <p>Now, I want to add a column (c3) to the composite primary key of Table T1.</p>
  
  <p>How can I do without dropping my primary key of Table T1?</p>