Elasticsearch索引聚合Aggregation

对于使用Elasticsearch来实现关系数据库中的group by操作，可以使用Aggregation，（本文纯手打，由于该用例是17年实现的，所以谅解，只是给大家提供思路)

简单举例：Elasticsearch5

//自己去实现client

TransportClient client = null;

//定义SearchRequestBuilder

SearchRequestBuilder sBuilder = client.prepareSearch("cars").setType("info");

//select color,count(1) as color_count form table1 group by color

TermsAggregationBuilder teamColorAgg = AggregationBuilders.terms("color_count").field("color");

sBuilder.addAggregation(teamColorAgg);

SearchResponse response = sBuilder.execute().actionGet();

Map<String,Aggregation> aggMap = response.getAggregations().asMap();

Terms terms = (Terms)aggMap.get("color_count");

List<Terms.Bucket> list = terms.getBuckets();

int size = list.size();

Terms.Bucket bucket = null;

for(int i=0;i<size;i++){

　　bucket = list.get(i); 

　　System.out.println(bucket.getKey()); //自己加断点看一下结果就好

}

//多字段的嵌套分组带条件的聚合

//select color,max(price) as max_price from table1 group by color

sBuilder.addAggregation(teamColorAgg);就是在执行这段代码之前多定义一些Aggregation

MaxAggregationBuilder pirceAgg= AggregationBuilders.max("max_price").field("price");

sBuilder.addAggregation(teamColorAgg.subAggregation(pirceAgg))); //subAggregation(?) 支持多种聚合类型，例如SumAggregation

//本人实际项目是支持灵活多级自定义嵌套分组，已经实现