title: DynamoDB scan on seconday index (GSI)
body: <p>I was reading the documentation on Scan and it prefaces with:</p>
  
  <blockquote>
    <p>The Scan operation returns one or more items and item attributes by accessing every item in a table or a secondary index.<a href="https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Scan.html" rel="nofollow noreferrer">1</a></p>
  </blockquote>
  
  <p>It made me wonder, under what circumstances would scanning a secondary index return a different set of records that the plain table would return?</p>
  
  <p>Scan does not support KeyConditionExpression, only FilterExpression - which basically happens after the data has been retrieved.</p>
  
  <p>So what would be the implication of scanning a GSI vs the table?</p>