add docs for aggregation function datasketches_hll_union_agg

docs/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md

@@ -0,0 +1,95 @@
+---
+{
+  "title": "DATASKETCHES_HLL_UNION_AGG",
+  "language": "en",
+  "description": "The datasketches_hll_union_agg function is an aggregate function used to union multiple Apache DataSketches HLL sketches and return the estimated cardinality of the union."
+}
+---
+
+## Description
+
+`datasketches_hll_union_agg` is an aggregate function used to **union** multiple Apache DataSketches **HLL** (`hll_sketch`) serialized values and return the **estimated cardinality** (approximate distinct count / NDV) after union.
+
+This function expects the input to be **serialized bytes of a DataSketches HLL sketch** (for example, generated by `hll_sketch.serialize_compact()` in the DataSketches library). It does not accept arbitrary strings.
+
+Aliases:
+
+- `ds_hll_union_count`
+- `ds_cardinality`
+
+## Syntax
+
+```sql
+datasketches_hll_union_agg(<sketch>)
+```
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<sketch>` | The serialized bytes of an Apache DataSketches HLL sketch. Supported types: STRING / VARCHAR / BINARY / VARBINARY. NULL values are ignored. Empty strings are treated as invalid input and will throw an error. |
+
+## Return Value
+
+Returns a BIGINT cardinality estimate value.  
+If there is no valid data in the group, returns 0.  
+If the input bytes cannot be deserialized as a valid DataSketches HLL sketch (including empty string), an error is thrown.
+
+## Example
+
+```sql
+-- setup
+CREATE TABLE test_datasketches_hll_union_agg_tbl (
+    id INT,
+    sk STRING
+)
+DISTRIBUTED BY HASH(id) BUCKETS 1
+PROPERTIES ("replication_num" = "1");
+
+-- The sketch bytes are inserted via Base64 decoding.
+INSERT INTO test_datasketches_hll_union_agg_tbl VALUES
+    (1, from_base64('AgEHCAMIBwjL18IEK/L7BoYv+Q11gWYHgbxdBntl5gj8LUIK')),
+    (2, from_base64('AwEHCAUIAAkKAAAAIjvrBcS1nwfGGWoEyHokBO8t9wc1qTEENkcJB7hWqQxZf9QNnuSbGA==')),
+    (3, NULL);
+```
+
+```sql
+SELECT datasketches_hll_union_agg(sk) FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------+
+| datasketches_hll_union_agg(sk) |
++-------------------------------+
+|                            17 |
++-------------------------------+
+```
+
+```sql
+-- aliases
+SELECT
+    datasketches_hll_union_agg(sk),
+    ds_hll_union_count(sk),
+    ds_cardinality(sk)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```sql
+-- empty input returns 0
+SELECT datasketches_hll_union_agg(sk)
+FROM test_datasketches_hll_union_agg_tbl
+WHERE sk IS NULL;
+```
+
+```text
++-------------------------------+
+| datasketches_hll_union_agg(sk) |
++-------------------------------+
+|                             0 |
++-------------------------------+
+```
+
+```sql
+-- empty string is invalid and will throw
+SELECT datasketches_hll_union_agg('');
+```

i18n/zh-CN/docusaurus-plugin-content-docs/current/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md

@@ -0,0 +1,94 @@
+---
+{
+  "title": "DATASKETCHES_HLL_UNION_AGG",
+  "language": "zh-CN",
+  "description": "datasketches_hll_union_agg 函数是一种聚合函数，用于对多个 Apache DataSketches HLL sketch 的序列化结果进行 union 合并，并返回合并后基数的估算值（近似去重数）。"
+}
+---
+
+## 描述
+
+`datasketches_hll_union_agg` 函数是一种聚合函数，用于对多个 **Apache DataSketches HLL sketch（hll_sketch）** 的序列化结果进行 **union 合并**，并返回合并后基数的**估算值**（近似去重数 / NDV）。
+
+该函数的输入不是普通字符串，而是 **DataSketches HLL sketch 的序列化字节串**（例如由 DataSketches 的 `hll_sketch.serialize_compact()` 生成）。
+
+别名：
+
+- `ds_hll_union_count`
+- `ds_cardinality`
+
+## 语法
+
+```sql
+datasketches_hll_union_agg(<sketch>)
+```
+
+## 参数
+
+| 参数 | 说明 |
+| -- | -- |
+| `<sketch>` | DataSketches HLL sketch 的序列化字节串。支持类型：STRING / VARCHAR / BINARY / VARBINARY。NULL 会被忽略；空字符串属于非法输入，将报错。 |
+
+## 返回值
+
+返回 BIGINT 类型的基数估算值。  
+如果组内没有合法数据则返回 0 。  
+若输入字节串无法反序列化为合法的 DataSketches HLL sketch（包括空字符串），将报错。
+
+## 举例
+
+```sql
+-- setup
+CREATE TABLE test_datasketches_hll_union_agg_tbl (
+    id INT,
+    sk STRING
+) DISTRIBUTED BY HASH(id) BUCKETS 1
+PROPERTIES ("replication_num" = "1");
+
+-- 通过 from_base64() 将 Base64 文本解码为 sketch 字节串后写入
+INSERT INTO test_datasketches_hll_union_agg_tbl VALUES
+    (1, from_base64('AgEHCAMIBwjL18IEK/L7BoYv+Q11gWYHgbxdBntl5gj8LUIK')),
+    (2, from_base64('AwEHCAUIAAkKAAAAIjvrBcS1nwfGGWoEyHokBO8t9wc1qTEENkcJB7hWqQxZf9QNnuSbGA==')),
+    (3, NULL);
+```
+
+```sql
+SELECT datasketches_hll_union_agg(sk) FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------+
+| datasketches_hll_union_agg(sk) |
++-------------------------------+
+|                            17 |
++-------------------------------+
+```
+
+```sql
+-- 别名用法
+SELECT
+    datasketches_hll_union_agg(sk),
+    ds_hll_union_count(sk),
+    ds_cardinality(sk)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```sql
+-- 组内无合法数据返回 0
+SELECT datasketches_hll_union_agg(sk)
+FROM test_datasketches_hll_union_agg_tbl
+WHERE sk IS NULL;
+```
+
+```text
++-------------------------------+
+| datasketches_hll_union_agg(sk) |
++-------------------------------+
+|                             0 |
++-------------------------------+
+```
+
+```sql
+-- 空字符串属于非法输入，将报错
+SELECT datasketches_hll_union_agg('');
+```

sidebars.ts

@@ -1973,6 +1973,7 @@ const sidebars: SidebarsConfig = {
                                 'sql-manual/sql-functions/aggregate-functions/count-by-enum',
                                 'sql-manual/sql-functions/aggregate-functions/covar',
                                 'sql-manual/sql-functions/aggregate-functions/covar-samp',
+                                'sql-manual/sql-functions/aggregate-functions/datasketches-hll-union-agg',
                                 'sql-manual/sql-functions/aggregate-functions/group-array-intersect',
                                 'sql-manual/sql-functions/aggregate-functions/group-array-union',
                                 'sql-manual/sql-functions/aggregate-functions/group-bit-and',