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Google Cloud BigQuery Transfer Operator to Postgres
===================================================

`Google Cloud BigQuery <https://cloud.google.com/bigquery>`__ is Google Cloud's serverless
data warehouse offering.
`PostgreSQL <https://www.postgresql.org/>`__ is an open-source relational database management system.
This operator can be used to copy data from a BigQuery table to PostgreSQL.


Prerequisite Tasks
^^^^^^^^^^^^^^^^^^

.. include:: /operators/_partials/prerequisite_tasks.rst

.. _howto/operator:BigQueryToPostgresOperator:

Operator
^^^^^^^^

Copying data from BigQuery table to Postgres table is performed with the
:class:`~airflow.providers.google.cloud.transfers.bigquery_to_postgres.BigQueryToPostgresOperator` operator.

Use :ref:`Jinja templating <concepts:jinja-templating>` with
:template-fields:`airflow.providers.google.cloud.transfers.bigquery_to_postgres.BigQueryToPostgresOperator`
to define values dynamically.

You may use the parameter ``selected_fields`` to limit the fields to be copied (all fields by default),
as well as the parameter ``replace`` to overwrite the destination table instead of appending to it.
If the ``replace`` parameter is used, then both ``selected_fields`` and ``replace_index`` parameters will
need to be specified due to constraints of the PostgreSQL's ON CONFLICT clause in the underlying INSERT
command.

For more information, please refer to the links above.

Transferring data
-----------------

The following Operator copies data from a BigQuery table to PostgreSQL.

.. exampleinclude:: /../../google/tests/system/google/cloud/bigquery/example_bigquery_to_postgres.py
    :language: python
    :dedent: 4
    :start-after: [START howto_operator_bigquery_to_postgres]
    :end-before: [END howto_operator_bigquery_to_postgres]

The Operator can also replace data in a PostgreSQL table with matching data from a BigQuery table.

.. exampleinclude:: /../../google/tests/system/google/cloud/bigquery/example_bigquery_to_postgres.py
    :language: python
    :dedent: 4
    :start-after: [START howto_operator_bigquery_to_postgres_upsert]
    :end-before: [END howto_operator_bigquery_to_postgres_upsert]


Reference
^^^^^^^^^

For further information, look at:

* `Google Cloud BigQuery Documentation <https://cloud.google.com/bigquery/docs/>`__
* `PostgreSQL Documentation <https://www.postgresql.org/docs/>`__
