elasticsearch多字段聚合实现方式

# 1、背景
我们知道在sql中是可以实现 group by 字段a,字段b，那么这种效果在elasticsearch中该如何实现呢？此处我们记录在elasticsearch中的3种方式来实现这个效果。

2、实现多字段聚合的思路

图片来源：https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-terms-aggregation.html
从上图中，我们可以知道，可以通过3种方式来实现 多字段的聚合操作。

3、需求

根据省(province)和性别(sex)来进行聚合，然后根据聚合后的每个桶的数据，在根据每个桶中的最大年龄(age)来进行倒序排序。

4、数据准备

4.1 创建索引

PUT /index_person
{
  "settings": {
    "number_of_shards": 1
  },
  "mappings": {
    "properties": {
      "id": {
        "type": "long"
      },
      "name": {
        "type": "keyword"
      },
      "province": {
        "type": "keyword"
      },
      "sex": {
        "type": "keyword"
      },
      "age": {
        "type": "integer"
      },
      "address": {
        "type": "text",
        "analyzer": "ik_max_word",
        "fields": {
          "keyword": {
            "type": "keyword",
            "ignore_above": 256
          }
        }
      }
    }
  }
}

4.2 准备数据

PUT /_bulk
{"create":{"_index":"index_person","_id":1}}
{"id":1,"name":"张三","sex":"男","age":20,"province":"湖北","address":"湖北省黄冈市罗田县匡河镇"}
{"create":{"_index":"index_person","_id":2}}
{"id":2,"name":"李四","sex":"男","age":19,"province":"江苏","address":"江苏省南京市"}
{"create":{"_index":"index_person","_id":3}}
{"id":3,"name":"王武","sex":"女","age":25,"province":"湖北","address":"湖北省武汉市江汉区"}
{"create":{"_index":"index_person","_id":4}}
{"id":4,"name":"赵六","sex":"女","age":30,"province":"北京","address":"北京市东城区"}
{"create":{"_index":"index_person","_id":5}}
{"id":5,"name":"钱七","sex":"女","age":16,"province":"北京","address":"北京市西城区"}
{"create":{"_index":"index_person","_id":6}}
{"id":6,"name":"王八","sex":"女","age":45,"province":"北京","address":"北京市朝阳区"}

5、实现方式

5.1 multi_terms实现

5.1.1 dsl

GET /index_person/_search
{
  "size": 0,
  "aggs": {
    "agg_province_sex": {
      "multi_terms": {
        "size": 10,
        "shard_size": 25,
        "order":{
          "max_age": "desc"    
        },
        "terms": [
          {
            "field": "province",
            "missing": "defaultProvince"
          },
          {
            "field": "sex"
          }
        ]
      },
      "aggs": {
        "max_age": {
          "max": {
            "field": "age"
          }
        }
      }
    }
  }
}

5.1.2 java 代码

    @Test
    @DisplayName("多term聚合-根据省和性别聚合，然后根据最大年龄倒序")
    public void agg01() throws IOException {

        SearchRequest searchRequest = new SearchRequest.Builder()
                .size(0)
                .index("index_person")
                .aggregations("agg_province_sex", agg ->
                        agg.multiTerms(multiTerms ->
                                        multiTerms.terms(term -> term.field("province"))
                                                .terms(term -> term.field("sex"))
                                                .order(new NamedValue<>("max_age", SortOrder.Desc))
                                )
                                .aggregations("max_age", ageAgg ->
                                        ageAgg.max(max -> max.field("age")))

                )
                .build();
        System.out.println(searchRequest);
        SearchResponse