Elasticsearch中的聚合查询，类似SQL的SUM/AVG/COUNT/GROUP BY分组查询，主要用于统计分析场景。

实例：

import org.apache.http.HttpHost;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.index.query.*;
import org.elasticsearch.search.aggregations.AggregationBuilders;
import org.elasticsearch.search.aggregations.Aggregations;
import org.elasticsearch.search.aggregations.bucket.terms.Terms;
import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
import org.elasticsearch.search.aggregations.metrics.Avg;
import org.elasticsearch.search.builder.SearchSourceBuilder;import java.io.IOException;public class Main {public static void main(String[] args) throws IOException {// 首先创建RestClient，后续章节通过RestClient对象进行参数配置。RestClientBuilder restClientBuilder = RestClient.builder(new HttpHost("localhost", 9200, "http"), // 设置ES服务地址，支持多个new HttpHost("localhost", 9201, "http"));// 创建RestHighLevelClient，请求都是通过RestHighLevelClient实例发出去的。RestHighLevelClient client = new RestHighLevelClient(restClientBuilder);// 创建SearchRequest对象, 设置查询索引名=orderSearchRequest searchRequest = new SearchRequest("order");// 通过SearchSourceBuilder构建搜索参数SearchSourceBuilder builder = new SearchSourceBuilder();// 通过QueryBuilders构建ES查询条件，这里查询所有文档，复杂的查询语句设置请参考前面的章节。builder.query(QueryBuilders.matchAllQuery());// 创建terms桶聚合，聚合名字=by_shop, 字段=shop_id，根据shop_id分组TermsAggregationBuilder aggregationBuilder = AggregationBuilders.terms("by_shop").field("shop_id");// 嵌套聚合// 设置Avg指标聚合，聚合名字=avg_price, 字段=price，计算平均价格aggregationBuilder.subAggregation(AggregationBuilders.avg("avg_price").field("price"));// 设置聚合查询builder.aggregation(aggregationBuilder);// 设置搜索条件searchRequest.source(builder);// 如果只想返回聚合统计结果，不想返回查询结果可以将分页大小设置为0builder.size(0);// 执行ES请求SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);// 处理聚合查询结果Aggregations aggregations = searchResponse.getAggregations();// 根据by_shop名字查询terms聚合结果Terms byShopAggregation = aggregations.get("by_shop");// 遍历terms聚合结果for (Terms.Bucket bucket  : byShopAggregation.getBuckets()) {// 因为是根据shop_id分组，因此可以直接将桶的key转换成int类型int shopId = bucket.getKeyAsNumber().intValue();// 根据avg_price聚合名字，获取嵌套聚合结果Avg avg = bucket.getAggregations().get("avg_price");// 获取平均价格double avgPrice = avg.getValue();}// 关闭ES Clientclient.close();}
}

例子聚合统计的效果等价SQL：

select shop_id, avg(price) as avg_price from order group by shop_id