需求：
（1）首先按照country国家来进行分组
（2）然后在每个country分组内，再按照入职年限进行分组
（3）最后计算每个分组内的平均薪资

1、重新设置field的类型属性

PUT /company
{
  "mappings": {
      "employee": {
        "properties": {
          "age": {
            "type": "long"
          },
          "country": {
            "type": "text",
            "fields": {
              "keyword": {
                "type": "keyword",
                "ignore_above": 256
              }
            },
            "fielddata": true
          },
          "join_date": {
            "type": "date"
          },
          "name": {
            "type": "text",
            "fields": {
              "keyword": {
                "type": "keyword",
                "ignore_above": 256
              }
            }
          },
          "position": {
            "type": "text",
            "fields": {
              "keyword": {
                "type": "keyword",
                "ignore_above": 256
              }
            }
          },
          "salary": {
            "type": "long"
          }
        }
      }
    }
}

2、使用restful api

GET /company/employee/_search
{
  "size": 0,
  "aggs": {
    "group_by_country": {
      "terms": {
        "field": "country"
      },
      "aggs": {
        "group_by_join_date": {
          "date_histogram": {
            "field": "join_date",
            "interval": "year"
          },
          "aggs": {
            "avg_salary": {
              "avg": {
                "field": "salary"
              }
            }
          }
        }
      }
    }
  }
}

3、使用java api

package com.roncoo.es.score.first;

import java.net.InetAddress;
import java.util.Iterator;
import java.util.Map;

import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.transport.TransportClient;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.InetSocketTransportAddress;
import org.elasticsearch.search.aggregations.Aggregation;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramInterval;
import org.elasticsearch.search.aggregations.bucket.histogram.Histogram;
import org.elasticsearch.search.aggregations.bucket.terms.StringTerms;
import org.elasticsearch.search.aggregations.bucket.terms.Terms.Bucket;
import org.elasticsearch.search.aggregations.metrics.avg.Avg;
import org.elasticsearch.transport.client.PreBuiltTransportClient;

/**
 * 员工聚合分析应用程序
 * @author Administrator
 *
 */
public class EmployeeAggrApp {

    @SuppressWarnings({ "unchecked", "resource" })
    public static void main(String[] args) throws Exception {
        Settings settings = Settings.builder()
                .put("cluster.name", "elasticsearch")
                .build();
        
        TransportClient client = new PreBuiltTransportClient(settings)
                .addTransportAddress(new InetSocketTransportAddress(InetAddress.getByName("localhost"), 9300)); 
        
        SearchResponse searchResponse = client.prepareSearch("company") 
                .addAggregation(AggregationBuilders.terms("group_by_country").field("country")
                        .subAggregation(AggregationBuilders
                                .dateHistogram("group_by_join_date")
                                .field("join_date")
                                .dateHistogramInterval(DateHistogramInterval.YEAR)
                                .subAggregation(AggregationBuilders.avg("avg_salary").field("salary")))
                )
                .execute().actionGet();
        
        Map<String, Aggregation> aggrMap = searchResponse.getAggregations().asMap();
        
        StringTerms groupByCountry = (StringTerms) aggrMap.get("group_by_country");
        Iterator<Bucket> groupByCountryBucketIterator = groupByCountry.getBuckets().iterator();
        while(groupByCountryBucketIterator.hasNext()) {
            Bucket groupByCountryBucket = groupByCountryBucketIterator.next();
            System.out.println(groupByCountryBucket.getKey() + ":" + groupByCountryBucket.getDocCount()); 
        
            Histogram groupByJoinDate = (Histogram) groupByCountryBucket.getAggregations().asMap().get("group_by_join_date");
            Iterator<org.elasticsearch.search.aggregations.bucket.histogram.Histogram.Bucket> groupByJoinDateBucketIterator = groupByJoinDate.getBuckets().iterator();
            while(groupByJoinDateBucketIterator.hasNext()) {
                org.elasticsearch.search.aggregations.bucket.histogram.Histogram.Bucket groupByJoinDateBucket = groupByJoinDateBucketIterator.next();
                System.out.println(groupByJoinDateBucket.getKey() + ":" +groupByJoinDateBucket.getDocCount()); 
            
                Avg avg = (Avg) groupByJoinDateBucket.getAggregations().asMap().get("avg_salary"); 
                System.out.println(avg.getValue()); 
            }
        }
        
        client.close();
    }
    
}