diff --git a/docs/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md b/docs/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
new file mode 100644
index 0000000000000..90eb8de35488a
--- /dev/null
+++ b/docs/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
@@ -0,0 +1,118 @@
+---
+{
+"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 as a DOUBLE value."
+}
+---
+
+## 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_estimate`
+- `datasketches_hll_estimate`
+
+## Syntax
+
+```sql
+datasketches_hll_union_agg(<sketch>)
+```
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<sketch>` | The serialized bytes of an Apache DataSketches HLL sketch. Supported types: STRING / VARCHAR / VARBINARY. NULL values are ignored. Empty strings are treated as invalid input and will throw an error. |
+
+## Return Value
+
+Returns a DOUBLE (Float64) cardinality estimate value.  
+If there is no valid data in the group (or the input is empty), returns 0.  
+If the input bytes cannot be deserialized as a valid DataSketches HLL sketch (including empty string), an error is thrown (typically with error code `CORRUPTION`).
+
+## 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
+-- The function returns DOUBLE, so use ROUND/CAST if you want an integer display.
+SELECT CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------------------------------+
+| CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) |
++-------------------------------------------------------+
+|                                                    17 |
++-------------------------------------------------------+
+```
+
+```sql
+-- aliases
+SELECT
+    CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) AS v1,
+    CAST(ROUND(ds_hll_estimate(sk)) AS BIGINT)            AS v2,
+    CAST(ROUND(datasketches_hll_estimate(sk)) AS BIGINT)  AS v3
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++------+------+------+
+| v1   | v2   | v3   |
++------+------+------+
+|   17 |   17 |   17 |
++------+------+------+
+```
+
+```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
+-- invalid sketch bytes will throw
+SELECT datasketches_hll_union_agg(from_base64('AA=='));
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: Attempt to deserialize unknown object type
+```
+
+```sql
+-- empty string is invalid and will throw
+SELECT datasketches_hll_union_agg('');
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: empty input.
+```
\ No newline at end of file
diff --git a/i18n/zh-CN/docusaurus-plugin-content-docs/current/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md b/i18n/zh-CN/docusaurus-plugin-content-docs/current/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
new file mode 100644
index 0000000000000..b4e54b4817f0d
--- /dev/null
+++ b/i18n/zh-CN/docusaurus-plugin-content-docs/current/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
@@ -0,0 +1,118 @@
+---
+{
+  "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（DOUBLE）。"
+}
+---
+
+## 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_estimate`
+- `datasketches_hll_estimate`
+
+## 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 / VARBINARY。NULL 会被忽略；空字符串属于非法输入，将报错。 |
+
+## 返回值
+
+返回 DOUBLE（Float64）类型的基数估算值。  
+如果没有合法数据（例如全为 NULL，或表为空）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（通常错误码为 `CORRUPTION`）。
+
+## 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
+-- 该函数返回 DOUBLE，如需以整数形式展示可配合 ROUND/CAST
+SELECT CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------------------------------+
+| CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) |
++-------------------------------------------------------+
+|                                                    17 |
++-------------------------------------------------------+
+```
+
+```sql
+-- 别名用法
+SELECT
+    CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) AS v1,
+    CAST(ROUND(ds_hll_estimate(sk)) AS BIGINT)            AS v2,
+    CAST(ROUND(datasketches_hll_estimate(sk)) AS BIGINT)  AS v3
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++------+------+------+
+| v1   | v2   | v3   |
++------+------+------+
+|   17 |   17 |   17 |
++------+------+------+
+```
+
+```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
+-- 非法 sketch 字节串将报错
+SELECT datasketches_hll_union_agg(from_base64('AA=='));
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: Attempt to deserialize unknown object type
+```
+
+```sql
+-- 空字符串属于非法输入，将报错
+SELECT datasketches_hll_union_agg('');
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: empty input.
+```
\ No newline at end of file
diff --git a/i18n/zh-CN/docusaurus-plugin-content-docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md b/i18n/zh-CN/docusaurus-plugin-content-docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
new file mode 100644
index 0000000000000..5d1960fa90781
--- /dev/null
+++ b/i18n/zh-CN/docusaurus-plugin-content-docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
@@ -0,0 +1,120 @@
+---
+{
+  "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（DOUBLE）。"
+}
+---
+
+> 从 4.1.2 版本开始支持。
+
+## 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_estimate`
+- `datasketches_hll_estimate`
+
+## 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 / VARBINARY。NULL 会被忽略；空字符串属于非法输入，将报错。 |
+
+## 返回值
+
+返回 DOUBLE（Float64）类型的基数估算值。  
+如果没有合法数据（例如全为 NULL，或表为空）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（通常错误码为 `CORRUPTION`）。
+
+## 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
+-- 该函数返回 DOUBLE，如需以整数形式展示可配合 ROUND/CAST
+SELECT CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------------------------------+
+| CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) |
++-------------------------------------------------------+
+|                                                    17 |
++-------------------------------------------------------+
+```
+
+```sql
+-- 别名用法
+SELECT
+    CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) AS v1,
+    CAST(ROUND(ds_hll_estimate(sk)) AS BIGINT)            AS v2,
+    CAST(ROUND(datasketches_hll_estimate(sk)) AS BIGINT)  AS v3
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++------+------+------+
+| v1   | v2   | v3   |
++------+------+------+
+|   17 |   17 |   17 |
++------+------+------+
+```
+
+```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
+-- 非法 sketch 字节串将报错
+SELECT datasketches_hll_union_agg(from_base64('AA=='));
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: Attempt to deserialize unknown object type
+```
+
+```sql
+-- 空字符串属于非法输入，将报错
+SELECT datasketches_hll_union_agg('');
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: empty input.
+```
\ No newline at end of file
diff --git a/sidebars.ts b/sidebars.ts
index 327afb8a2831c..8edfc219570bc 100644
--- a/sidebars.ts
+++ b/sidebars.ts
@@ -1997,6 +1997,7 @@ 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/exponential-moving-average',
                                 'sql-manual/sql-functions/aggregate-functions/group-array-intersect',
                                 'sql-manual/sql-functions/aggregate-functions/group-array-union',
diff --git a/versioned_docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md b/versioned_docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
new file mode 100644
index 0000000000000..9c2d1dea1f059
--- /dev/null
+++ b/versioned_docs/version-4.x/sql-manual/sql-functions/aggregate-functions/datasketches_hll_union_agg.md
@@ -0,0 +1,120 @@
+---
+{
+    "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 as a DOUBLE value."
+}
+---
+
+> Supported since version 4.1.2.
+
+## 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.
+
+## Alias
+
+- `ds_hll_estimate`
+- `datasketches_hll_estimate`
+
+## Syntax
+
+```sql
+datasketches_hll_union_agg(<sketch>)
+```
+
+## Parameters
+
+| Parameter | Description |
+| -- | -- |
+| `<sketch>` | The serialized bytes of an Apache DataSketches HLL sketch. Supported types: STRING / VARCHAR / VARBINARY. NULL values are ignored. Empty strings are treated as invalid input and will throw an error. |
+
+## Return Value
+
+Returns a DOUBLE (Float64) cardinality estimate value.  
+If there is no valid data in the group (or the input is empty), returns 0.  
+If the input bytes cannot be deserialized as a valid DataSketches HLL sketch (including empty string), an error is thrown (typically with error code `CORRUPTION`).
+
+## 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
+-- The function returns DOUBLE, so use ROUND/CAST if you want an integer display.
+SELECT CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT)
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++-------------------------------------------------------+
+| CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) |
++-------------------------------------------------------+
+|                                                    17 |
++-------------------------------------------------------+
+```
+
+```sql
+-- aliases
+SELECT
+    CAST(ROUND(datasketches_hll_union_agg(sk)) AS BIGINT) AS v1,
+    CAST(ROUND(ds_hll_estimate(sk)) AS BIGINT)            AS v2,
+    CAST(ROUND(datasketches_hll_estimate(sk)) AS BIGINT)  AS v3
+FROM test_datasketches_hll_union_agg_tbl;
+```
+
+```text
++------+------+------+
+| v1   | v2   | v3   |
++------+------+------+
+|   17 |   17 |   17 |
++------+------+------+
+```
+
+```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
+-- invalid sketch bytes will throw
+SELECT datasketches_hll_union_agg(from_base64('AA=='));
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: Attempt to deserialize unknown object type
+```
+
+```sql
+-- empty string is invalid and will throw
+SELECT datasketches_hll_union_agg('');
+```
+
+```text
+ERROR 1105 (HY000): errCode = 2, detailMessage = (127.0.0.1)[CORRUPTION]HLL sketch data corrupted when add: empty input.
+```
\ No newline at end of file
diff --git a/versioned_sidebars/version-4.x-sidebars.json b/versioned_sidebars/version-4.x-sidebars.json
index a329bbc91ae9c..57c240ad928d0 100644
--- a/versioned_sidebars/version-4.x-sidebars.json
+++ b/versioned_sidebars/version-4.x-sidebars.json
@@ -2168,6 +2168,7 @@
                     "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",