feat(bigquery): add bigquery_federated_view_schema_cloud_sql sample to inspect Cloud SQL table schema via federated query (#14735)

Problem:
The BigQuery documentation (https://cloud.google.com/bigquery/docs/cloud-sql-federated-queries)
needs a standalone, tested Python code sample demonstrating how to
inspect Cloud SQL table schema via federated query (region tag `bigquery_federated_view_schema_cloud_sql`).

Solution:
- Add `federated_view_schema_cloud_sql(project_id: str, connection_id: str) -> None` in `bigquery/federated_queries/bigquery_federated_view_schema_cloud_sql.py`
  (Query information_schema.columns in a Cloud SQL database from BigQuery using EXTERNAL_QUERY.)
- Add unit tests (`bigquery/federated_queries/bigquery_federated_view_schema_cloud_sql_test.py`) covering both the success
  path and API error handling (`GoogleAPICallError`)

Author: iennae

bigquery/federated_queries/bigquery_federated_view_schema_cloud_sql.py

@@ -0,0 +1,74 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# [START bigquery_federated_view_schema_cloud_sql]
+import sys
+
+from google.api_core import exceptions
+from google.cloud import bigquery
+
+
+def federated_view_schema_cloud_sql(
+    project_id: str,
+    connection_id: str,
+) -> None:
+    """Views a Cloud SQL table schema from BigQuery using EXTERNAL_QUERY.
+
+    Args:
+        project_id: Google Cloud project ID (for example, 'example-project').
+        connection_id: Fully qualified BigQuery Cloud SQL connection ID
+            (for example, 'example-project.us.example-cloudsql-conn').
+    """
+    client = bigquery.Client(project=project_id)
+    # Query Cloud SQL information_schema.columns inside EXTERNAL_QUERY to inspect table column metadata.
+    external_sql = (
+        "SELECT column_name, data_type, is_nullable "
+        "FROM information_schema.columns "
+        "WHERE table_name = 'orders' "
+        "ORDER BY ordinal_position ASC"
+    )
+    query = f"""
+        SELECT
+          column_name,
+          data_type,
+          is_nullable
+        FROM EXTERNAL_QUERY('{connection_id}', "{external_sql}")
+        ORDER BY column_name ASC;
+    """
+
+    try:
+        print(f"Inspecting Cloud SQL table schema via connection: {connection_id}")
+        query_job = client.query(query)
+        rows = list(query_job.result())
+    except exceptions.NotFound as err:
+        print(
+            f"error: Cloud SQL connection '{connection_id}' not found in project "
+            f"'{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+    except exceptions.GoogleAPICallError as err:
+        print(
+            f"error: could not inspect Cloud SQL table schema on connection "
+            f"'{connection_id}' in project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+
+    print(f"Resource ID: {connection_id}")
+    print(f"Columns Returned: {len(rows)}")
+    print(f"Job ID: {query_job.job_id}")
+
+
+# [END bigquery_federated_view_schema_cloud_sql]

bigquery/federated_queries/bigquery_federated_view_schema_cloud_sql_test.py

@@ -0,0 +1,69 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from unittest import mock
+
+import bigquery_federated_view_schema_cloud_sql
+from google.api_core import exceptions
+import pytest
+
+
+def test_federated_view_schema_cloud_sql_success(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    mock_client = mock.MagicMock()
+    mock_job = mock.MagicMock()
+    mock_job.job_id = "example-job-123"
+    mock_job.result.return_value = [mock.MagicMock(), mock.MagicMock()]
+    mock_client.query.return_value = mock_job
+    monkeypatch.setattr(
+        bigquery_federated_view_schema_cloud_sql.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_federated_view_schema_cloud_sql.federated_view_schema_cloud_sql(
+        project_id="example-project",
+        connection_id="example-project.us.example-cloudsql-conn",
+    )
+
+    captured = capsys.readouterr()
+    assert "Resource ID: example-project.us.example-cloudsql-conn" in captured.out
+    assert "Columns Returned: 2" in captured.out
+    assert mock_client.query.called
+
+
+def test_federated_view_schema_cloud_sql_error(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    mock_client = mock.MagicMock()
+    mock_job = mock.MagicMock()
+    mock_job.result.side_effect = exceptions.NotFound("connection not found")
+    mock_client.query.return_value = mock_job
+    monkeypatch.setattr(
+        bigquery_federated_view_schema_cloud_sql.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_federated_view_schema_cloud_sql.federated_view_schema_cloud_sql(
+        project_id="example-project",
+        connection_id="example-project.us.example-cloudsql-conn",
+    )
+
+    captured = capsys.readouterr()
+    assert "error:" in captured.err
+    assert "example-cloudsql-conn" in captured.err