title: Add ANOTHER primary key to a table which is UNIQUE
body: <p>I'm having problems with adding another primary key to my table. 
  I have 3 columns:</p>
  
  <ol>
  <li>Account ID (Identity)</li>
  <li>EmailID </li>
  <li>Data field</li>
  </ol>
  
  <p>When I made the table I had this to make the Account ID and the Email ID unique.</p>
  
  <pre><code>PRIMARY KEY (AccountID, EmailID)
  </code></pre>
  
  <p>I thought that would make my emailid unique, but then after I tried inserting another row with the same emailid it went through.
  So I thought I missed something out. </p>
  
  <p>Now for my question:</p>
  
  <ol>
  <li>IF, I had to use alter, how do I alter the table/PK Constraint to modify the EmailID field and make it Unique?</li>
  <li>IF I decided to drop the table and made a new one, how do I make those two primary keys unique?</li>
  </ol>