Here's how we will find the maximum value of the downloadTotal field in the entire index/type:

GET bigginsight/_search
{
 "aggregations": {                    
    "download_max": {                  
      "max": {                         
        "field": "downloadTotal"       
      }      
    }
  },
  "size": 0                            
}

These aggregations were really simple. Now, let's look at some more advanced stats and extended stats aggregations.