HLL_COUNT_EXTRACT

注意事项

HLL_COUNT_EXTRACT/HLL_COUNT_MERGE/HLL_COUNT_MERGE_PARTIAL函数使用的BINARY数据需要来源于HLL_COUNT_INIT函数， 不能来源于其他系统或者其他方式。

命令格式

BIGINT HLL_COUNT_EXTRACT(BINARY <sketch>)

参数说明

sketch：必填，BINARY类型。HLL++ sketch，由HLL_COUNT_INIT函数生成。

返回值说明

返回BIGINT类型的基数估计值。如果输入sketch为 NULL， 返回0。

使用示例

查询每个国家中至少有一张发票的自然人数量。

SELECT
  country,
  HLL_COUNT_EXTRACT(HLL_sketch) AS distinct_customers_with_open_invoice
FROM
  (
    SELECT
    country,
    HLL_COUNT_INIT(customer_id) AS hll_sketch
    FROM values
      ('UA', 'customer_id_1', 'invoice_id_11'),
      ('BR', 'customer_id_3', 'invoice_id_31'),
      ('CZ', 'customer_id_2', 'invoice_id_22'),
      ('CZ', 'customer_id_2', 'invoice_id_23'),
      ('BR', 'customer_id_3', 'invoice_id_31'),
      ('UA', 'customer_id_2', 'invoice_id_24')
    t(country, customer_id, invoice_id)
    GROUP BY country
  );

返回结果：

+---------+--------------------------------------+
| country | distinct_customers_with_open_invoice |
+---------+--------------------------------------+
| BR      | 1                                    |
| CZ      | 1                                    |
| UA      | 2                                    |
+---------+--------------------------------------+

相关函数

HLL_COUNT_EXTRACT函数属于HyperLogLog++函数，MaxCompute支持一系列近似聚合的HyperLogLog++函数，更多相关函数请参见HyperLogLog++函数。