title: Converting table index from Int to Bigint MySQL
body: <p>I've been running a small web-based experiemnt using Facebook UIDs to verify unique users.</p>
  
  <p>Recently I've discovered that UIDs can be bigger than I realised among some users, so my int-based system is now inadequate and I need to convert to bigint.</p>
  
  <p>I can't risk losing the results I already have, but need to convert the table so that the index containing the uid is now bigint. Are there any particular issues changing the type of an index column, and would it be as simple as:</p>
  
  <pre><code>ALTER TABLE breadusers MODIFY userid bigint;
  </code></pre>
  
  <p>?</p>