ES中对应的SQL的count(distinct 列名) java实现

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

　

/**
     * 查询去重后总量
     * @param req
     * @param field  es里字段名称
     * @return
     */
    private Integer countDistinct(String field){
        // 创建查询请求对象
        SearchRequest searchRequest = new SearchRequest(INDEX_NAME);
        // 创建查询资源对象
        SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
15         // 查询条件-分组
        CardinalityAggregationBuilder cardinalityAggregationBuilder = AggregationBuilders.cardinality(field).field(field);
        sourceBuilder.aggregation(cardinalityAggregationBuilder);
        sourceBuilder.size(0);
        searchRequest.source(sourceBuilder);

        SearchResponse searchResponse = null;
        int size = 0;
        try {
            searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);
            if(null == searchResponse){ return 0; }
            ParsedCardinality parsedCardinality = searchResponse.getAggregations().get(field);　　// 这个field就是上面起的别名
            size = (int) parsedCardinality.getValue();
        } catch (IOException e) {
            log.debug("ES查询分组条数有误！");
        }
        return size;
    }