[docs](from-unixtime) add fractional timestamp support documentation (#3543)

- Document support for DECIMAL type input timestamps with fractional
seconds
- Update parameter description to indicate BIGINT or DECIMAL type
support
- Extend supported timestamp range to include microsecond precision
(253402271999.999999)
- Add three examples demonstrating fractional timestamp conversion with
sub-second precision

## Versions 

- [x] dev
- [x] 4.x
- [ ] 3.x
- [ ] 2.1

## Languages

- [x] Chinese
- [x] English

## Docs Checklist

- [x] Checked by AI
- [ ] Test Cases Built

Author: zclllyybb

docs/sql-manual/sql-functions/scalar-functions/date-time-functions/from-unixtime.md

@@ -9,7 +9,7 @@
 ## Description
 
 
-The FROM_UNIXTIME function is used to convert a Unix timestamp (in seconds) to a date-time string or VARCHAR type value in a specified format. The reference time for Unix timestamps is 1970-01-01 00:00:00 UTC, and the function generates the corresponding date-time representation based on the input timestamp and format string.
+The FROM_UNIXTIME function is used to convert a Unix timestamp (in seconds) to a date-time string or VARCHAR type value in a specified format. The reference time for Unix timestamps is 1970-01-01 00:00:00 UTC, and the function generates the corresponding date-time representation based on the input timestamp and format string. When the input timestamp contains a fractional part, the result includes sub-second precision up to microseconds (6 decimal places).
 
 This function is consistent with the [from_unixtime function](https://dev.mysql.com/doc/refman/8.4/en/date-and-time-functions.html#function_from-unixtime) in MySQL.
 
@@ -23,13 +23,13 @@ FROM_UNIXTIME(<unix_timestamp> [, <string_format>])
 
 | Parameter | Description |
 | -- | -- |
-| `<unix_timestamp>` | Input Unix timestamp, of integer type BIGINT, representing the number of seconds from 1970-01-01 00:00:00 UTC |
+| `<unix_timestamp>` | Input Unix timestamp, of type BIGINT or DECIMAL, representing the number of seconds (with optional fractional seconds) from 1970-01-01 00:00:00 UTC |
 | `<string_format>` | Format string, supports varchar and string types, default is %Y-%m-%d %H:%i:%s. For specific formats, please refer to [date-format](./date-format) |
 
 ## Return Value
 
-Returns date in specified format, of type VARCHAR, returning the result of converting the UTC timezone unix timestamp to the current timezone time.
-- Currently supported unix_timestamp range is [0, 253402271999] corresponding to dates from 1970-01-01 00:00:00 to 9999-12-31 23:59:59, unix_timestamp outside this range will return an error
+Returns date in specified format, of type VARCHAR, returning the result of converting the UTC timezone unix timestamp to the current timezone time. When the input contains a fractional part, the result includes sub-second precision (e.g., `2007-12-01 00:30:19.500000`).
+- Currently supported unix_timestamp range is [0, 253402271999.999999] corresponding to dates from 1970-01-01 00:00:00 to 9999-12-31 23:59:59.999999, unix_timestamp outside this range will return an error
 - If string_format is invalid, returns a string that does not meet expectations.
 - If any parameter is NULL, returns NULL
 - If the format length is over 128 characters, returns error
@@ -95,6 +95,30 @@ mysql> select from_unixtime(32536799,"gdaskpdp");
 | gdaskpdp                           |
 +------------------------------------+
 
+---Fractional timestamp input, result includes sub-second precision
+mysql> select from_unixtime(1196440219.5);
++-----------------------------+
+| from_unixtime(1196440219.5) |
++-----------------------------+
+| 2007-12-01 00:30:19.500000  |
++-----------------------------+
+
+---Fractional timestamp with microsecond precision
+mysql> select from_unixtime(1196440219.123456);
++----------------------------------+
+| from_unixtime(1196440219.123456) |
++----------------------------------+
+| 2007-12-01 00:30:19.123456       |
++----------------------------------+
+
+---Use %f format specifier to display microseconds explicitly
+mysql> select from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f');
++----------------------------------------------------------+
+| from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f') |
++----------------------------------------------------------+
+| 2007-12-01 00:30:19.123456                               |
++----------------------------------------------------------+
+
 ---Input is NULL, returns NULL
 mysql> select from_unixtime(NULL);
 +---------------------+

i18n/zh-CN/docusaurus-plugin-content-docs/current/sql-manual/sql-functions/scalar-functions/date-time-functions/from-unixtime.md

@@ -8,7 +8,7 @@
 
 ## 描述
 
-FROM_UNIXTIME 函数用于将 Unix 时间戳（以秒为单位） 转换为指定格式的日期时间字符串或 VARCHAR 类型值。Unix 时间戳的基准时间为 1970-01-01 00:00:00 UTC，函数会根据输入的时间戳和格式字符串，生成对应的日期时间表示。
+FROM_UNIXTIME 函数用于将 Unix 时间戳（以秒为单位） 转换为指定格式的日期时间字符串或 VARCHAR 类型值。Unix 时间戳的基准时间为 1970-01-01 00:00:00 UTC，函数会根据输入的时间戳和格式字符串，生成对应的日期时间表示。当输入的时间戳包含小数部分时，结果将包含最多微秒精度（6 位小数）的亚秒部分。
 
 该函数与 mysql 中的 [from_unixtime 函数](https://dev.mysql.com/doc/refman/8.4/en/date-and-time-functions.html#function_from-unixtime) 行为一致
 
@@ -22,13 +22,13 @@ FROM_UNIXTIME(<unix_timestamp> [, <string_format>])
 
 | 参数 | 说明 |
 | -- | -- |
-| `<unix_timestamp>` | 输入的 Unix 时间戳，类型为整数 BIGINT，表示从 1970-01-01 00:00:00 UTC 开始的秒数 |
+| `<unix_timestamp>` | 输入的 Unix 时间戳，类型为 BIGINT 或 DECIMAL，表示从 1970-01-01 00:00:00 UTC 开始的秒数（可包含小数秒） |
 | `<string_format>` | format 格式，支持类型 varchar 和 string，默认为 %Y-%m-%d %H:%i:%s，具体格式请查看 [date-format](./date-format)|
 
 ## 返回值
 
-返回指定格式的日期，类型为 VARCHAR，返回的是 UTC 时区下的时间戳的时间戳转换为当前时区的时间。
-- 目前支持的 unix_timestamp 范围为 [0，253402271999] 对应日期为 1970-01-01 00:00:00 至 9999-12-31 23:59:59，超出范围的 unix_timestamp 将返回错误
+返回指定格式的日期，类型为 VARCHAR，返回的是 UTC 时区下的时间戳转换为当前时区的时间。当输入包含小数部分时，结果包含亚秒精度（如 `2007-12-01 00:30:19.500000`）。
+- 目前支持的 unix_timestamp 范围为 [0，253402271999.999999] 对应日期为 1970-01-01 00:00:00 至 9999-12-31 23:59:59.999999，超出范围的 unix_timestamp 将返回错误
 - 若 string_format 格式无效，返回不符合预期的字符串。
 - 若任意参数为 NULL，则返回 NULL
 - 如果 string_format 超过 128 字符长度，返回错误
@@ -93,6 +93,30 @@ mysql> select from_unixtime(32536799,"gdaskpdp");
 | gdaskpdp                           |
 +------------------------------------+
 
+---小数时间戳输入，结果包含亚秒精度
+mysql> select from_unixtime(1196440219.5);
++-----------------------------+
+| from_unixtime(1196440219.5) |
++-----------------------------+
+| 2007-12-01 00:30:19.500000  |
++-----------------------------+
+
+---小数时间戳，微秒精度
+mysql> select from_unixtime(1196440219.123456);
++----------------------------------+
+| from_unixtime(1196440219.123456) |
++----------------------------------+
+| 2007-12-01 00:30:19.123456       |
++----------------------------------+
+
+---使用 %f 格式符显式输出微秒部分
+mysql> select from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f');
++----------------------------------------------------------+
+| from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f') |
++----------------------------------------------------------+
+| 2007-12-01 00:30:19.123456                               |
++----------------------------------------------------------+
+
 ---输入为 NULL，返回 NULL
 mysql> select from_unixtime(NULL);
 +---------------------+

i18n/zh-CN/docusaurus-plugin-content-docs/version-4.x/sql-manual/sql-functions/scalar-functions/date-time-functions/from-unixtime.md

@@ -8,7 +8,7 @@
 
 ## 描述
 
-FROM_UNIXTIME 函数用于将 Unix 时间戳（以秒为单位） 转换为指定格式的日期时间字符串或 VARCHAR 类型值。Unix 时间戳的基准时间为 1970-01-01 00:00:00 UTC，函数会根据输入的时间戳和格式字符串，生成对应的日期时间表示。
+FROM_UNIXTIME 函数用于将 Unix 时间戳（以秒为单位） 转换为指定格式的日期时间字符串或 VARCHAR 类型值。Unix 时间戳的基准时间为 1970-01-01 00:00:00 UTC，函数会根据输入的时间戳和格式字符串，生成对应的日期时间表示。当输入的时间戳包含小数部分时，结果将包含最多微秒精度（6 位小数）的亚秒部分。
 
 该函数与 mysql 中的 [from_unixtime 函数](https://dev.mysql.com/doc/refman/8.4/en/date-and-time-functions.html#function_from-unixtime) 行为一致
 
@@ -22,13 +22,13 @@ FROM_UNIXTIME(<unix_timestamp> [, <string_format>])
 
 | 参数 | 说明 |
 | -- | -- |
-| `<unix_timestamp>` | 输入的 Unix 时间戳，类型为整数 BIGINT，表示从 1970-01-01 00:00:00 UTC 开始的秒数 |
+| `<unix_timestamp>` | 输入的 Unix 时间戳，类型为 BIGINT 或 DECIMAL，表示从 1970-01-01 00:00:00 UTC 开始的秒数（可包含小数秒） |
 | `<string_format>` | format 格式，支持类型 varchar 和 string，默认为 %Y-%m-%d %H:%i:%s，具体格式请查看 [date-format](./date-format)|
 
 ## 返回值
 
-返回指定格式的日期，类型为 VARCHAR，返回的是 UTC 时区下的时间戳的时间戳转换为当前时区的时间。
-- 目前支持的 unix_timestamp 范围为 [0，253402271999] 对应日期为 1970-01-01 00:00:00 至 9999-12-31 23:59:59，超出范围的 unix_timestamp 将返回错误
+返回指定格式的日期，类型为 VARCHAR，返回的是 UTC 时区下的时间戳转换为当前时区的时间。当输入包含小数部分时，结果包含亚秒精度（如 `2007-12-01 00:30:19.500000`）。
+- 目前支持的 unix_timestamp 范围为 [0，253402271999.999999] 对应日期为 1970-01-01 00:00:00 至 9999-12-31 23:59:59.999999，超出范围的 unix_timestamp 将返回错误
 - 若 string_format 格式无效，返回不符合预期的字符串。
 - 若任意参数为 NULL，则返回 NULL
 - 如果 string_format 超过 128 字符长度，返回错误
@@ -93,6 +93,30 @@ mysql> select from_unixtime(32536799,"gdaskpdp");
 | gdaskpdp                           |
 +------------------------------------+
 
+---小数时间戳输入，结果包含亚秒精度
+mysql> select from_unixtime(1196440219.5);
++-----------------------------+
+| from_unixtime(1196440219.5) |
++-----------------------------+
+| 2007-12-01 00:30:19.500000  |
++-----------------------------+
+
+---小数时间戳，微秒精度
+mysql> select from_unixtime(1196440219.123456);
++----------------------------------+
+| from_unixtime(1196440219.123456) |
++----------------------------------+
+| 2007-12-01 00:30:19.123456       |
++----------------------------------+
+
+---使用 %f 格式符显式输出微秒部分
+mysql> select from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f');
++----------------------------------------------------------+
+| from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f') |
++----------------------------------------------------------+
+| 2007-12-01 00:30:19.123456                               |
++----------------------------------------------------------+
+
 ---输入为 NULL，返回 NULL
 mysql> select from_unixtime(NULL);
 +---------------------+

versioned_docs/version-4.x/sql-manual/sql-functions/scalar-functions/date-time-functions/from-unixtime.md

@@ -9,7 +9,7 @@
 ## Description
 
 
-The FROM_UNIXTIME function is used to convert a Unix timestamp (in seconds) to a date-time string or VARCHAR type value in a specified format. The reference time for Unix timestamps is 1970-01-01 00:00:00 UTC, and the function generates the corresponding date-time representation based on the input timestamp and format string.
+The FROM_UNIXTIME function is used to convert a Unix timestamp (in seconds) to a date-time string or VARCHAR type value in a specified format. The reference time for Unix timestamps is 1970-01-01 00:00:00 UTC, and the function generates the corresponding date-time representation based on the input timestamp and format string. When the input timestamp contains a fractional part, the result includes sub-second precision up to microseconds (6 decimal places).
 
 This function is consistent with the [from_unixtime function](https://dev.mysql.com/doc/refman/8.4/en/date-and-time-functions.html#function_from-unixtime) in MySQL.
 
@@ -23,13 +23,13 @@ FROM_UNIXTIME(<unix_timestamp> [, <string_format>])
 
 | Parameter | Description |
 | -- | -- |
-| `<unix_timestamp>` | Input Unix timestamp, of integer type BIGINT, representing the number of seconds from 1970-01-01 00:00:00 UTC |
+| `<unix_timestamp>` | Input Unix timestamp, of type BIGINT or DECIMAL, representing the number of seconds (with optional fractional seconds) from 1970-01-01 00:00:00 UTC |
 | `<string_format>` | Format string, supports varchar and string types, default is %Y-%m-%d %H:%i:%s. For specific formats, please refer to [date-format](./date-format) |
 
 ## Return Value
 
-Returns date in specified format, of type VARCHAR, returning the result of converting the UTC timezone unix timestamp to the current timezone time.
-- Currently supported unix_timestamp range is [0, 253402271999] corresponding to dates from 1970-01-01 00:00:00 to 9999-12-31 23:59:59, unix_timestamp outside this range will return an error
+Returns date in specified format, of type VARCHAR, returning the result of converting the UTC timezone unix timestamp to the current timezone time. When the input contains a fractional part, the result includes sub-second precision (e.g., `2007-12-01 00:30:19.500000`).
+- Currently supported unix_timestamp range is [0, 253402271999.999999] corresponding to dates from 1970-01-01 00:00:00 to 9999-12-31 23:59:59.999999, unix_timestamp outside this range will return an error
 - If string_format is invalid, returns a string that does not meet expectations.
 - If any parameter is NULL, returns NULL
 - If the format length is over 128 characters, returns error
@@ -95,6 +95,30 @@ mysql> select from_unixtime(32536799,"gdaskpdp");
 | gdaskpdp                           |
 +------------------------------------+
 
+---Fractional timestamp input, result includes sub-second precision
+mysql> select from_unixtime(1196440219.5);
++-----------------------------+
+| from_unixtime(1196440219.5) |
++-----------------------------+
+| 2007-12-01 00:30:19.500000  |
++-----------------------------+
+
+---Fractional timestamp with microsecond precision
+mysql> select from_unixtime(1196440219.123456);
++----------------------------------+
+| from_unixtime(1196440219.123456) |
++----------------------------------+
+| 2007-12-01 00:30:19.123456       |
++----------------------------------+
+
+---Use %f format specifier to display microseconds explicitly
+mysql> select from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f');
++----------------------------------------------------------+
+| from_unixtime(1196440219.123456, '%Y-%m-%d %H:%i:%s.%f') |
++----------------------------------------------------------+
+| 2007-12-01 00:30:19.123456                               |
++----------------------------------------------------------+
+
 ---Input is NULL, returns NULL
 mysql> select from_unixtime(NULL);
 +---------------------+