一、需求：select count(distinct city_name)  from tableA;

二、代码：用的是cardinality基数统计，高版本API 

AggregationBuilders.cardinality(field).field(field);  // 第一个field是聚合的别名，别名就是下面根据这个别名获取聚合结果 第二个是ES里的字段

　

 1 /**
 2      * 查询去重后总量
 3      * @param req
 4      * @param field  es里字段名称
 5      * @return
 6      */
 7     private Integer countDistinct(String field){
 8         // 创建查询请求对象
 9         SearchRequest searchRequest = new SearchRequest(INDEX_NAME);
10         // 创建查询资源对象
11         SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
12 15         // 查询条件-分组
16         CardinalityAggregationBuilder cardinalityAggregationBuilder = AggregationBuilders.cardinality(field).field(field);
17         sourceBuilder.aggregation(cardinalityAggregationBuilder);
18         sourceBuilder.size(0);
19         searchRequest.source(sourceBuilder);
20 
21         SearchResponse searchResponse = null;
22         int size = 0;
23         try {
24             searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
25             if(null == searchResponse){ return 0; }
26             ParsedCardinality parsedCardinality = searchResponse.getAggregations().get(field);　　// 这个field就是上面起的别名
27             size = (int) parsedCardinality.getValue();
28         } catch (IOException e) {
29             log.debug("ES查询分组条数有误！");
30         }
31         return size;
32     }