title: AWS DynamoDB count query results without retrieving
body: <p>I would like to check how many entries are in a DynamoDB table that matches a query <em>without retrieving the actual entries</em>, using boto3.</p>
  
  <p>I want to run a machine learning job on data from DynamoDB table. The data I'm training on is a data that answers a query, <strong>not the entire table</strong>. I want to run the job only if I have enough data to train on.
  Therefore, I want to check if I want to check that I have enough entries that match the query.
  It is worth mentioning that the DynamoDB table I'm querying is <em>really big</em>, therefore actual retrieving is no option unless I actually want to run the job.</p>
  
  <p>I know that I can use <code>boto3.dynamodb.describe_table()</code> to get how many entries there are in the <em>entire table</em>, but as I mentioned earlier, I want to know only how many entries match a query.</p>
  
  <p>Any ideas?</p>