sum and stats.sum return different values when doc_count is 0.

[walterra]

Elasticsearch version: 7.0.0-alpha1-SNAPSHOT, Build: 9e36764/2017-10-03T12:16:42.018Z

Plugins installed: [x-pack]

JVM version: 1.8.0_144

OS version: macOS 10.13

Description of the problem including expected versus actual behavior:

You get different results for e.g. a distinct sum aggregation vs. the sum within the stats aggregation. For a doc_count of 0, the sum aggregation returns 0 whereas the sum within the stats aggregation is null.

Steps to reproduce:

1. Create some documents:

PUT my_test/test/1
{
    "category" : "c1",
    "value": 1
}
PUT my_test/test/2
{
    "category" : "c2"
}
PUT my_test/test/3
{
    "category" : "c3",
    "value": 1
}
PUT my_test/test/4
{
    "category" : "c3",
    "value": 1
}

2. Run a nested aggregation:

POST my_test/_search
{
  "size": 0,
  "aggregations": {
    "categories": {
      "terms": {
        "field": "category.keyword"
      },
      "aggs": {
        "my_min": {
          "min": {
            "field": "value"
          }
        },
        "my_max": {
          "max": {
            "field": "value"
          }
        },
        "my_avg": {
          "avg": {
            "field": "value"
          }
        },
        "my_sum": {
          "sum": {
            "field": "value"
          }
        },
        "my_stats": {
          "stats": {
            "field": "value"
          }
        }
      }
    }
  }
}

3. The result looks like this:

  "aggregations": {
    "categories": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": [
        {
          "key": "c3",
          "doc_count": 2,
          "my_stats": {
            "count": 2,
            "min": 1,
            "max": 1,
            "avg": 1,
            "sum": 2
          },
          "my_max": {
            "value": 1
          },
          "my_avg": {
            "value": 1
          },
          "my_min": {
            "value": 1
          },
          "my_sum": {
            "value": 2
          }
        },
        {
          "key": "c1",
          "doc_count": 1,
          "my_stats": {
            "count": 1,
            "min": 1,
            "max": 1,
            "avg": 1,
            "sum": 1
          },
          "my_max": {
            "value": 1
          },
          "my_avg": {
            "value": 1
          },
          "my_min": {
            "value": 1
          },
          "my_sum": {
            "value": 1
          }
        },
        {
          "key": "c2",
          "doc_count": 1,
          "my_stats": {
            "count": 0,
            "min": null,
            "max": null,
            "avg": null,
            "sum": null
          },
          "my_max": {
            "value": null
          },
          "my_avg": {
            "value": null
          },
          "my_min": {
            "value": null
          },
          "my_sum": {
            "value": 0
          }
        }
      ]
    }
  }

The document in category c2 doesn't include the value field. All the aggregation results have a value of null whereas only the sum aggregation has a value of 0.

[colings86]

We should change the Stats aggregation so the value of stats.sum when no documents are collected is 0 like value_count

[PammyS]

I will be happy to fix this issue! Please assign it to me

[colings86]

@PammyS We are not able to assign issues to users that are not part of the Elastic org but we would love it if you are able to work on this fix. Please feel most welcome to open a PR. Thanks