ES中對應的SQL的count(distinct 列名) java實現

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

二、代碼：用的是cardinality基數統計，高版本API 

AggregationBuilders.cardinality(field).field(field);  // 第一個field是聚合的別名，別名就是下面根據這個別名獲取聚合結果 第二個是ES里的字段

　

/**
     * 查詢去重后總量
     * @param req
     * @param field  es里字段名稱
     * @return
     */
    private Integer countDistinct(String field){
        // 創建查詢請求對象
        SearchRequest searchRequest = new SearchRequest(INDEX_NAME);
        // 創建查詢資源對象
        SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
15         // 查詢條件-分組
        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);　　// 這個field就是上面起的別名
            size = (int) parsedCardinality.getValue();
        } catch (IOException e) {
            log.debug("ES查詢分組條數有誤！");
        }
        return size;
    }