Elasticsearch索引聚合Aggregation

對於使用Elasticsearch來實現關系數據庫中的group by操作，可以使用Aggregation，（本文純手打，由於該用例是17年實現的，所以諒解，只是給大家提供思路)

簡單舉例：Elasticsearch5

//自己去實現client

TransportClient client = null;

//定義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()); //自己加斷點看一下結果就好

}

//多字段的嵌套分組帶條件的聚合

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

sBuilder.addAggregation(teamColorAgg);就是在執行這段代碼之前多定義一些Aggregation

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

sBuilder.addAggregation(teamColorAgg.subAggregation(pirceAgg))); //subAggregation(?) 支持多種聚合類型，例如SumAggregation

//本人實際項目是支持靈活多級自定義嵌套分組，已經實現