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Unloading Data from Databend

Unloading data refers to the process of extracting or transferring data stored in a database to another storage location. This can involve exporting data from the database to a file or another database, or copying data from the database to a backup or archiving system.

Databend recommends using the COPY INTO <location> command to export your data to a Stage or an external location as a file in one of the supported formats. This command is a convenient and efficient way to transfer data out of the database and into a file for further processing or analysis.

For more information about the command, see COPY INTO <location>. To view the list of supported file formats that can be used to save the exported data, see Input & Output File Formats.

Tutorial - Unload to an External Stage​

In this tutorial, you will first create an external stage and then use the COPY INTO command to export the result of a query as a parquet file to the external stage.

Step 1. Create External Stage​

Create an external stage named unload with the CREATE STAGE command:

CREATE STAGE unload url='s3://unload/files/' connection=(aws_key_id='1a2b3c' aws_secret_key='4x5y6z');
备注

The COPY INTO command works for both internal and external stages. Create the one you need to proceed. To learn more about the Databend stage, see Stage.

Step 2. Export Data​

Export the query result as a parquet file to the external stage unload:

COPY INTO @unload FROM (SELECT * FROM numbers(10000000)) FILE_FORMAT = (TYPE = PARQUET);

Step 3. Verify Export File​

Show the exported file with the LIST STAGE command:

LIST @unload;
+--------------------------------------------------------+----------+------------------------------------+-------------------------------+---------+
| name                                                   | size     | md5                                | last_modified                 | creator |
+--------------------------------------------------------+----------+------------------------------------+-------------------------------+---------+
| data_8799a438-9788-4dcb-bd45-3aa23ea9c6a3_32_0.parquet | 41486538 | "F187251F37666928684DBED4AF0523DF" | 2023-02-12 03:45:03.000 +0000 | NULL    |
+--------------------------------------------------------+----------+------------------------------------+-------------------------------+---------+

You can also query the exported data to confirm its validity:

SELECT sum(number) FROM @unload (PATTERN => '.*parquet');
+----------------+
| sum(number)    |
+----------------+
| 49999995000000 |
+----------------+