Create ds_hll_count_distinct.md

Signed-off-by: 絵空事スピリット <[email protected]>

docs/zh/sql-reference/sql-functions/aggregate-functions/ds_hll_count_distinct.md

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+# ds_hll_count_distinct
+
+返回聚合函数的近似值，结果类似于 COUNT(DISTINCT col)。相似函数为 APPROX_COUNT_DISTINCT(expr)。
+
+相较于 COUNT DISTINCT 速度更快，并且使用固定大小的内存，因此基于高基数列使用时内存占用更少。
+
+相较于 APPROX_COUNT_DISTINCT(expr) 速度更慢，但由于 Apache Datasketches 的优势，导致其精度更高。更多信息，参考 [HyperLogLog Sketches](https://datasketches.apache.org/docs/HLL/HllSketches.html)。
+
+## 语法
+
+```Haskell
+ds_hll_count_distinct(expr, [log_k], [tgt_type])
+```
+- `log_k`：必须为整数。范围：[4, 21]。默认值：17。
+- `tgt_type`：有效值为 `HLL_4`、`HLL_6`（默认）以及 `HLL_8`。
+
+## 示例
+
+```plain text
+mysql> CREATE TABLE t1 (
+    ->   id BIGINT NOT NULL,
+    ->   province VARCHAR(64),
+    ->   age SMALLINT,
+    ->   dt VARCHAR(10) NOT NULL
+    -> )
+    -> DUPLICATE KEY(id)
+    -> DISTRIBUTED BY HASH(id) BUCKETS 4;
+Query OK, 0 rows affected (0.02 sec)
+mysql> insert into t1 select generate_series, generate_series, generate_series % 100, "2024-07-24" from table(generate_series(1, 100000));
+Query OK, 100000 rows affected (0.29 sec)
+mysql> select ds_hll_count_distinct(id), ds_hll_count_distinct(province), ds_hll_count_distinct(age), ds_hll_count_distinct(dt) from t1 order by 1, 2;
++---------------------------+---------------------------------+----------------------------+---------------------------+
+| ds_hll_count_distinct(id) | ds_hll_count_distinct(province) | ds_hll_count_distinct(age) | ds_hll_count_distinct(dt) |
++---------------------------+---------------------------------+----------------------------+---------------------------+
+|                    100090 |                          100140 |                        100 |                         1 |
++---------------------------+---------------------------------+----------------------------+---------------------------+
+1 row in set (0.07 sec)
+mysql> select ds_hll_count_distinct(id, 21), ds_hll_count_distinct(province, 21), ds_hll_count_distinct(age, 21), ds_hll_count_distinct(dt, 21) from t1 order by 1, 2;
++-------------------------------+-------------------------------------+--------------------------------+-------------------------------+
+| ds_hll_count_distinct(id, 21) | ds_hll_count_distinct(province, 21) | ds_hll_count_distinct(age, 21) | ds_hll_count_distinct(dt, 21) |
++-------------------------------+-------------------------------------+--------------------------------+-------------------------------+
+|                         99995 |                              100001 |                            100 |                             1 |
++-------------------------------+-------------------------------------+--------------------------------+-------------------------------+
+1 row in set (0.07 sec)
+mysql> select ds_hll_count_distinct(id, 10, "HLL_8"), ds_hll_count_distinct(province, 10, "HLL_8"), ds_hll_count_distinct(age, 10, "HLL_8"), ds_hll_count_distinct(dt, 10, "HLL_8") from t1 order by 1, 2;
++----------------------------------------+----------------------------------------------+-----------------------------------------+----------------------------------------+
+| ds_hll_count_distinct(id, 10, 'HLL_8') | ds_hll_count_distinct(province, 10, 'HLL_8') | ds_hll_count_distinct(age, 10, 'HLL_8') | ds_hll_count_distinct(dt, 10, 'HLL_8') |
++----------------------------------------+----------------------------------------------+-----------------------------------------+----------------------------------------+
+|                                  99844 |                                       101905 |                                      96 |                                      1 |
++----------------------------------------+----------------------------------------------+-----------------------------------------+----------------------------------------+
+1 row in set (0.09 sec)
+```
+
+## Keywords
+
+DS_HLL_COUNT_DISTINCT,APPROX_COUNT_DISTINCT