title: Query size limits in DynamoDB
body: <p>I don't get the concept of limits for query/scan in DynamoDb.
  According to the docs:</p>
  
  <blockquote>
    <p>A single Query operation can retrieve a maximum of 1 MB of data.This
    limit applies before any FilterExpression is applied to the results.</p>
  </blockquote>
  
  <p>Let's say I have 10k items, 250kb per item, all of them fit query params.</p>
  
  <ol>
  <li>If I run a simple query, I get only 4 items?</li>
  <li>If I use ProjectionExpression to retrieve only single attribute (1kb
      in size), will I get 1k items?</li>
  <li>If I only need to count items (select: 'COUNT'), will it count all
      items (10k)?</li>
  </ol>