title: amazon-dynamodb and filtering by date
body: <p>I have a dynamodb table which has a GlobalSecondaryIndex with a date field as attribute of keytype "range". Values are stored in ISO-format "YYYY-MM-DD".
  I want to access in node only records with dates greater than a certain date.
  It seems to work with a parameter for my query:</p>
  
  <pre><code>KeyConditionExpression: 'myDate &gt;= :myDate',
  ExpressionAttributeValues: {   
      ':myDate': '2017-11-17'
  }
  </code></pre>
  
  <p>However I do not quite understand. The date is technically speaking a string. Is it reliable to trust the string comparison or should it be done in a different way?</p>