title: DynamoDB most efficient date type
body: <p>I see that DynamoDB is essentially limited to <a href="http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DataModel.html#DataModel.DataTypes" rel="noreferrer">three data types</a>: String, Number, and Binary.  That seems to leave two options for storing a date or timestamp:</p>
  
  <ul>
  <li><strong>String</strong> of an 8601 date/time format or Unix timestamp</li>
  <li><strong>Number</strong> of a Unix timestamp</li>
  </ul>
  
  <p>I will need to 'sort' results by using this date/timestamp as a range key and using scanIndexForward.  Is it possible to say which approach would be more efficient?</p>