docs(transforming): add data load transform

Author: BohuTANG

docs/doc/12-load-data/00-stage.md

@@ -1,6 +1,6 @@
 ---
-title: Tutorial - Load from an Internal Stage
-sidebar_label: Tutorial - Load from an Internal Stage
+title: Load from an Internal Stage
+sidebar_label: Load from an Internal Stage
 description:
   Load data from Databend stages.
 ---

docs/doc/12-load-data/01-s3.md

@@ -1,6 +1,6 @@
 ---
-title: Tutorial - Load from an Amazon S3 Bucket
-sidebar_label: Tutorial - Load from an Amazon S3 Bucket
+title: Load from an Amazon S3 Bucket
+sidebar_label: Load from an Amazon S3 Bucket
 description:
   Load data from Amazon S3.
 ---

docs/doc/12-load-data/02-local.md

@@ -1,6 +1,6 @@
 ---
-title: Tutorial - Load from a Local File
-sidebar_label: Tutorial - Load from a Local File
+title: Load from a Local File
+sidebar_label: Load from a Local File
 description:
   Load data from local file system.
 ---

docs/doc/12-load-data/04-http.md

@@ -1,6 +1,6 @@
 ---
-title: Tutorial - Load from Remote File
-sidebar_label: Tutorial - Load from a Remote File
+title: Load from Remote File
+sidebar_label: Load from a Remote File
 description:
   Load data from remote files.
 ---

docs/doc/12-load-data/05-data-load-transform.md

@@ -0,0 +1,86 @@
+---
+title: Transforming Data During a Load
+sidebar_label: Transforming Data During a Load
+description: Learn how to use Databend to transform data while loading it into a table using the COPY INTO <table> command. 
+---
+
+Databend supports transforming data while loading it into a table using the `COPY INTO <table>` command, which simplifies your ETL pipeline for basic transformations. 
+
+This feature helps you avoid the use of temporary tables to store pre-transformed data when reordering columns during a data load.
+
+The `COPY` command supports:
+- Column reordering, column omission, and casts using a SELECT statement. There is no requirement for your data files to have the same number and ordering of columns as your target table.
+
+:::note
+Transforming is only supported for Parquet format in the stage.
+:::
+
+## Load a Subset of Table Data
+
+Load a subset of data into a table. The following example loads data from columns `id`, `name` of a staged Parquet file:
+
+**Sample Data**
+```text
+id | name       | age
+---|------------|----
+ 1 | John Doe   |  35
+ 2 | Jane Smith |  28
+```
+
+**Example**
+```sql
+-- create a table
+CREATE TABLE my_table(id int, name string);
+
+COPY INTO my_table
+FROM (SELECT t.id, t.name FROM @mystage t)
+FILE_FORMAT = (type = parquet) PATTERN='.*parquet';
+````
+
+## Reorder Columns During a Load
+
+To reorder the columns from a staged Parquet file before loading it into a table, you can use the `COPY INTO` command with a `SELECT` statement. The following example reorders the columns `name` and `id`:
+
+**Sample Data**
+```text
+id | name       | age
+---|------------|----
+ 1 | John Doe   |  35
+ 2 | Jane Smith |  28
+```
+
+**Example**
+````sql
+CREATE TABLE my_table(name string, id int);
+
+COPY INTO my_table
+FROM (SELECT t.name, t.id FROM @mystage t)
+FILE_FORMAT = (type = parquet) PATTERN='.*parquet';
+````
+
+## Convert Data Types During a Load
+
+To convert staged data into other data types during a data load, you can use the appropriate conversion function in your `SELECT` statement.
+
+The following example converts a timestamp into a date:
+
+**Sample Data**
+```text
+id | name    | timestamp
+---|---------|--------------------
+ 1 | John Doe| 2022-03-15 10:30:00
+ 2 | Jane Doe| 2022-03-14 09:00:00
+```
+
+**Example**
+```sql
+CREATE TABLE my_table(id int, name string, time date);
+
+COPY INTO my_table
+FROM (SELECT t.id, t.name, to_date(t.timestamp) FROM @mystage t)
+FILE_FORMAT = (type = parquet) PATTERN='.*parquet';
+```
+
+## Conclusion
+
+Transforming data during a load is a powerful feature of Databend that allows you to simplify your ETL pipeline and avoid the use of temporary tables. With the ability to transform data during a load, you can streamline your ETL pipeline and focus on the analysis of your data rather than the mechanics of moving it around.