elasticsearch聚合系列之cardinality_elasticsearch cardinality

cardinality 即去重计算，类似sql中 count（distinct），先去重再求和，计算指定field值的种类数。

下面实例，计算有多少个不同的city。

请求：

POST bank/_doc/_search
{
  "size": 0,
  "aggs": {
    "cartinality_gender": {
      "cardinality": {
        "field": "city.keyword"
      }
    }
  }
}

响应：

{
  "took": 2,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 15,
    "max_score": 0,
    "hits": []
  },
  "aggregations": {
    "cartinality_gender": {
      "value": 15
    }
  }
}