ORDER BY doesn't work as expected on cardinality aggregations

[canberk-oguz]

I realized that ORDER BY doesn't work properly on COUNT(DISTINCT x) queries. Instead of adding the given sort field, it adds the _count field as a default sort field.

GET /_opendistro/_sql/_explain
{
  "query": "SELECT count(distinct id) as bal FROM accounts GROUP BY topic_id ORDER BY bal DESC"
}

Incorrect DSL:

{
  "from" : 0,
  "size" : 0,
  "_source" : {
    "includes" : [
      "COUNT"
    ],
    "excludes" : [ ]
  },
  "aggregations" : {
    "topic_id" : {
      "terms" : {
        "field" : "topic_id",
        "size" : 200,
        "min_doc_count" : 1,
        "shard_min_doc_count" : 0,
        "show_term_doc_count_error" : false,
        "order" : [
          {
            "_count" : "desc"
          },
          {
            "_key" : "asc"
          }
        ]
      },
      "aggregations" : {
        "bal" : {
          "cardinality" : {
            "field" : "id"
          }
        }
      }
    }
  }
}

Expected DSL:

{
  "from" : 0,
  "size" : 0,
  "_source" : {
    "includes" : [
      "COUNT"
    ],
    "excludes" : [ ]
  },
  "aggregations" : {
    "topic_id" : {
      "terms" : {
        "field" : "topic_id",
        "size" : 200,
        "min_doc_count" : 1,
        "shard_min_doc_count" : 0,
        "show_term_doc_count_error" : false,
        "order" : [
          {
            "bal" : "desc"
          },
          {
            "_key" : "asc"
          }
        ]
      },
      "aggregations" : {
        "bal" : {
          "cardinality" : {
            "field" : "id"
          }
        }
      }
    }
  }
}

[penghuo]

Thanks for reporting the issue. Will look into this.