Elasticsearch 聚合查询(Aggregation)详解

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=order
        SearchRequest 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0
        builder.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 Client
        client.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