title: Cassandra alter column type: which types are compatible?
body: <p>There's some patchy information on the interwebs about some examples when column type can't be changed. For example, on the <a href="http://docs.datastax.com/en/cql/3.0/cql/cql_reference/alter_table_r.html?scroll=reference_ds_xqq_hpc_xj__changing-the-type-of-a-column" rel="nofollow noreferrer" title="DataStax site">DataStax site</a> there's a mention:</p>
  
  <ul>
  <li>Changing the type of a clustering column. </li>
  <li>Changing columns on which
  an index is defined.</li>
  </ul>
  
  <p>Or, for example, <a href="https://stackoverflow.com/a/21539917/371804" title="here">here</a> is mentioned that you can't convert <code>uuid</code> to <code>timeuuid</code>. And from my personal experience, I can't change <code>text</code> to <code>timestamp</code> (we store dates in ISO8601 format as text, an unfortunate decision early in the project timeline).</p>
  
  <p>However, I can't find a full description of which types can be converted to which, or at least which types <em>can't</em> be converted to which. Does anyone know?</p>