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new 883ae8a86d [typo](docs) Add some content for bitmap_hash.md. (#17747)
883ae8a86d is described below
commit 883ae8a86d042233cb3bdde977284f5552db3f8b
Author: yagagagaga <[email protected]>
AuthorDate: Tue Mar 14 08:27:07 2023 +0800
[typo](docs) Add some content for bitmap_hash.md. (#17747)
---
.../sql-functions/bitmap-functions/bitmap_hash.md | 86 +++++++++++++++++++---
.../sql-functions/bitmap-functions/bitmap_hash.md | 86 +++++++++++++++++++---
2 files changed, 148 insertions(+), 24 deletions(-)
diff --git
a/docs/en/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
b/docs/en/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
index 1b19f5a07c..20a7324778 100644
--- a/docs/en/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
+++ b/docs/en/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
@@ -25,28 +25,90 @@ under the License.
-->
## bitmap_hash
-### description
+
+### Name
+
+BITMAP_HASH
+
+### Description
+
+Calculating hash value for what your input and return a BITMAP which contain
the hash value. MurMur3 is used for this function because it is
high-performance with low collision rate. More important, the MurMur3
distribution is "simili-random"; the Chi-Square distribution test is used to
prove it. By the way, Different hardware platforms and different SEED may
change the result of MurMur3. For more information about its performance, see
[Smhasher](http://rurban.github.io/smhasher/).
+
#### Syntax
-`BITMAP BITMAP_HASH(expr)`
+```
+BITMAP BITMAP_HASH(<any_value>)
+```
+
+#### Arguments
+
+`<any_value>`
+any value or expression.
+
+#### Return Type
+
+BITMAP
-Compute the 32-bits hash value of a expr of any type, then return a bitmap
containing that hash value. Mainly be used to load non-integer value into
bitmap column, e.g.,
+#### Remarks
+Generally, MurMurHash 32 is friendly to random, short STRING with low
collision rate about one-billionth. But for longer STRING, such as your path of
system, can cause more frequent collision. If you indexed your system path, you
will find a lot of collisions.
+
+The following two values are the same.
+
+```sql
+SELECT
bitmap_to_string(bitmap_hash('/System/Volumes/Data/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/System/Library/Frameworks/KernelManagement.framework/KernelManagement.tbd'))
AS a ,
+
bitmap_to_string(bitmap_hash('/System/Library/PrivateFrameworks/Install.framework/Versions/Current/Resources/es_419.lproj/Architectures.strings'))
AS b;
```
-cat data | curl --location-trusted -u user:passwd -T - -H "columns:
dt,page,device_id, device_id=bitmap_hash(device_id)"
http://host:8410/api/test/testDb/_stream_load
+
+Here is the result.
+
+```text
++-----------+-----------+
+| a | b |
++-----------+-----------+
+| 282251871 | 282251871 |
++-----------+-----------+
```
-### example
+### Example
+
+If you want to calculate MurMur3 of a certain value, you can
```
-mysql> select bitmap_count(bitmap_hash('hello'));
-+------------------------------------+
-| bitmap_count(bitmap_hash('hello')) |
-+------------------------------------+
-| 1 |
-+------------------------------------+
+select bitmap_to_array(bitmap_hash('hello'))[1];
```
-### keywords
+Here is the result.
+
+```text
++-------------------------------------------------------------+
+| %element_extract%(bitmap_to_array(bitmap_hash('hello')), 1) |
++-------------------------------------------------------------+
+| 1321743225 |
++-------------------------------------------------------------+
+```
+
+If you want to `count distinct` some columns, using bitmap has higher
performance in some scenes.
+
+```sql
+select bitmap_count(bitmap_union(bitmap_hash(`word`))) from `words`;
+```
+
+Here is the result.
+
+```text
++-------------------------------------------------+
+| bitmap_count(bitmap_union(bitmap_hash(`word`))) |
++-------------------------------------------------+
+| 33263478 |
++-------------------------------------------------+
+```
+
+### Keywords
BITMAP_HASH,BITMAP
+
+### Best Practice
+
+For more information, see also:
+- [BITMAP_HASH64](./bitmap_hash64.md)
diff --git
a/docs/zh-CN/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
b/docs/zh-CN/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
index 37496a45ed..c9d64f7ca3 100644
--- a/docs/zh-CN/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
+++ b/docs/zh-CN/docs/sql-manual/sql-functions/bitmap-functions/bitmap_hash.md
@@ -25,28 +25,90 @@ under the License.
-->
## bitmap_hash
-### description
+
+### Name
+
+BITMAP_HASH
+
+### Description
+
+对任意类型的输入，计算其 32 位的哈希值，并返回包含该哈希值的 bitmap。该函数使用的哈希算法为 MurMur3。MurMur3
算法是一种高性能的、低碰撞率的散列算法，其计算出来的值接近于随机分布，并且能通过卡方分布测试。需要注意的是，不同硬件平台、不同 Seed
值计算出来的散列值可能不同。关于此算法的性能可以参考 [Smhasher](http://rurban.github.io/smhasher/) 排行榜。
+
#### Syntax
-`BITMAP BITMAP_HASH(expr)`
+```
+BITMAP BITMAP_HASH(<any_value>)
+```
+
+#### Arguments
+
+`<any_value>`
+任何值或字段表达式。
+
+#### Return Type
+
+BITMAP
-对任意类型的输入计算32位的哈希值，返回包含该哈希值的bitmap。主要用于stream load任务将非整型字段导入Doris表的bitmap字段。例如
+#### Remarks
+一般来说，MurMur 32
位算法对于完全随机的、较短的字符串的散列效果较好，碰撞率能达到几十亿分之一，但对于较长的字符串，比如你的操作系统路径，碰撞率会比较高。如果你扫描你系统里的路径，就会发现碰撞率仅仅只能达到百万分之一甚至是十万分之一。
+
+下面两个字符串的 MurMur3 散列值是一样的：
+
+```sql
+SELECT
bitmap_to_string(bitmap_hash('/System/Volumes/Data/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/System/Library/Frameworks/KernelManagement.framework/KernelManagement.tbd'))
AS a ,
+
bitmap_to_string(bitmap_hash('/System/Library/PrivateFrameworks/Install.framework/Versions/Current/Resources/es_419.lproj/Architectures.strings'))
AS b;
```
-cat data | curl --location-trusted -u user:passwd -T - -H "columns:
dt,page,device_id, device_id=bitmap_hash(device_id)"
http://host:8410/api/test/testDb/_stream_load
+
+结果如下：
+
+```text
++-----------+-----------+
+| a | b |
++-----------+-----------+
+| 282251871 | 282251871 |
++-----------+-----------+
```
-### example
+### Example
+
+如果你想计算某个值的 MurMur3，你可以：
```
-mysql> select bitmap_count(bitmap_hash('hello'));
-+------------------------------------+
-| bitmap_count(bitmap_hash('hello')) |
-+------------------------------------+
-| 1 |
-+------------------------------------+
+select bitmap_to_array(bitmap_hash('hello'))[1];
```
-### keywords
+结果如下：
+
+```text
++-------------------------------------------------------------+
+| %element_extract%(bitmap_to_array(bitmap_hash('hello')), 1) |
++-------------------------------------------------------------+
+| 1321743225 |
++-------------------------------------------------------------+
+```
+
+如果你想统计某一列去重后的个数，可以使用位图的方式，某些场景下性能比 `count distinct` 好很多：
+
+```sql
+select bitmap_count(bitmap_union(bitmap_hash(`word`))) from `words`;
+```
+
+结果如下：
+
+```text
++-------------------------------------------------+
+| bitmap_count(bitmap_union(bitmap_hash(`word`))) |
++-------------------------------------------------+
+| 33263478 |
++-------------------------------------------------+
+```
+
+### Keywords
BITMAP_HASH,BITMAP
+
+### Best Practice
+
+还可参见
+- [BITMAP_HASH64](./bitmap_hash64.md)
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