docs: add examples for streaming load column mapping

Author: BohuTANG

docs/cn/guides/20-self-hosted/04-references/http-streaming-load.md

@@ -56,13 +56,34 @@ X-Databend-SQL: insert into demo.people(name,age,city) values (?, ?, 'BJ') from
 ### 列映射规则
 
 - **不写列清单，也不写 `VALUES`**：按表的列定义顺序写入（文件字段依次对应表列）。
+  - CSV 表头：`id,name,age`
+  - SQL：
+    ```text
+    X-Databend-SQL: insert into demo.people from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **写了列清单，但不写 `VALUES`**：按列清单的顺序写入（文件字段依次对应列清单）。
+  - CSV 表头：`id,name`
+  - SQL：
+    ```text
+    X-Databend-SQL: insert into demo.people(id,name) from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **写了列清单且写 `VALUES`**：
   - 每个目标列对应 `VALUES` 中的一个表达式。
   - `VALUES` 里的每个 `?` 会依次消费上传文件里的一个字段。
+  - CSV 表头：`name,age`
+  - SQL：
+    ```text
+    X-Databend-SQL: insert into demo.people(name,age,city) values (?, ?, 'BJ') from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **未提供的列**：
   - 如果该列有 `DEFAULT`，则使用默认值；
   - 否则写入 `NULL`（若列是 `NOT NULL` 则会失败）。
+- **只读取 CSV 的部分字段（忽略多余字段）**：
+  - 默认情况下，如果文件字段数多于目标列清单，会直接报错。
+  - 如需忽略多余字段，设置 `error_on_column_count_mismatch=false`：
+    ```text
+    X-Databend-SQL: insert into demo.people(id,name) from @_databend_load file_format=(type=csv skip_header=1 error_on_column_count_mismatch=false)
+    ```
 
 **cURL 模板：**
 
@@ -96,6 +117,7 @@ CSV 的解析规则通过 `FILE_FORMAT=(...)` 指定，语法与 Databend 的文
 - `field_delimiter=','`：字段分隔符（默认 `,`）。
 - `quote='\"'`：引用符号。
 - `record_delimiter='\n'`：行分隔符。
+- `error_on_column_count_mismatch=false`：允许列数不匹配并忽略多余字段。
 
 示例：
 

docs/en/guides/20-self-hosted/04-references/http-streaming-load.md

@@ -56,13 +56,34 @@ X-Databend-SQL: insert into demo.people(name,age,city) values (?, ?, 'BJ') from
 ### Column mapping rules
 
 - **No column list, no `VALUES`**: file fields map to table columns by table definition order.
+  - CSV header: `id,name,age`
+  - SQL:
+    ```text
+    X-Databend-SQL: insert into demo.people from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **With column list, no `VALUES`**: file fields map to the listed columns in order.
+  - CSV header: `id,name`
+  - SQL:
+    ```text
+    X-Databend-SQL: insert into demo.people(id,name) from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **With column list and `VALUES`**:
   - Each target column gets the corresponding expression in `VALUES`.
   - Each `?` consumes one field from the uploaded file, in order.
+  - CSV header: `name,age`
+  - SQL:
+    ```text
+    X-Databend-SQL: insert into demo.people(name,age,city) values (?, ?, 'BJ') from @_databend_load file_format=(type=csv skip_header=1)
+    ```
 - **Columns not provided**:
   - Use column `DEFAULT` value if defined.
   - Otherwise insert `NULL` (and fail if the column is `NOT NULL`).
+- **Read only part of a CSV (ignore extra fields)**:
+  - By default, Databend errors if the file has more fields than the target column list.
+  - To ignore extra fields, set `error_on_column_count_mismatch=false`:
+    ```text
+    X-Databend-SQL: insert into demo.people(id,name) from @_databend_load file_format=(type=csv skip_header=1 error_on_column_count_mismatch=false)
+    ```
 
 **cURL template:**
 
@@ -102,6 +123,7 @@ Common CSV options:
 - `field_delimiter=','`: Use a custom delimiter (default is `,`).
 - `quote='\"'`: Quote character.
 - `record_delimiter='\n'`: Line delimiter.
+- `error_on_column_count_mismatch=false`: Allow column count mismatch and ignore extra fields.
 
 Examples: