title: How to get columns' sql type queried by sqlalchemy
body: <p>For example:</p>
  
  <pre><code>sql = "select a, b, c from tb"
  rs = engine.execute(sql)
  </code></pre>
  
  <p>the columns' types in <code>rs.cursor.description</code> are python types, not sql types, so how can I get columns' sql types?</p>