feat(bigquery): add bigquery_query_external_bigtable sample to query Cloud Bigtable data as an external table

Problem:
The BigQuery documentation (https://cloud.google.com/bigquery/docs/external-data-bigtable)
needs a standalone, tested Python code sample demonstrating how to
query Cloud Bigtable data as an external table (region tag `bigquery_query_external_bigtable`).

Solution:
- Add `query_external_bigtable(project_id: str, bigtable_instance_id: str, bigtable_table_id: str) -> None` in `bigquery/biglake/bigquery_query_external_bigtable.py`
  (Configure a temporary Cloud Bigtable external table mapping column families and qualifiers and query it from BigQuery.)
- Add unit tests (`bigquery/biglake/bigquery_query_external_bigtable_test.py`) covering both the success
  path and API error handling (`GoogleAPICallError`)

Author: iennae

bigquery/biglake/bigquery_query_external_bigtable.py

@@ -0,0 +1,90 @@
+# 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_query_external_bigtable]
+import sys
+
+from google.api_core import exceptions
+from google.cloud import bigquery
+
+
+def query_external_bigtable(
+    project_id: str,
+    bigtable_instance_id: str,
+    bigtable_table_id: str,
+) -> None:
+    """Configures and queries a temporary BigQuery external table backed by Cloud Bigtable.
+
+    Args:
+        project_id: Google Cloud project ID (for example, 'example-project').
+        bigtable_instance_id: Cloud Bigtable instance ID hosting the source table
+            (for example, 'example-bt-instance').
+        bigtable_table_id: Cloud Bigtable table ID containing the column family
+            (for example, 'example_bt_table').
+    """
+    client = bigquery.Client(project=project_id)
+    temp_table_name = "example_bigtable_temp"
+    source_uri = (
+        f"https://googleapis.com/bigtable/projects/{project_id}"
+        f"/instances/{bigtable_instance_id}/tables/{bigtable_table_id}"
+    )
+
+    # Map the Cloud Bigtable column family into a temporary table definition for a single query job.
+    external_config = bigquery.ExternalConfig("BIGTABLE")
+    external_config.source_uris = [source_uri]
+    external_config.bigtable_options.read_rowkey_as_string = True
+    family = bigquery.BigtableColumnFamily()
+    family.family_id = "stats_summary"
+    family.type_ = "STRING"
+    family.encoding = "TEXT"
+    external_config.bigtable_options.column_families = [family]
+
+    job_config = bigquery.QueryJobConfig(
+        table_definitions={temp_table_name: external_config}
+    )
+    sql = f"""
+        SELECT
+          rowkey,
+          stats_summary
+        FROM `{temp_table_name}`
+        ORDER BY rowkey ASC
+        LIMIT 10;
+    """
+
+    try:
+        print(f"Querying temporary Cloud Bigtable table mapped to {source_uri}")
+        query_job = client.query(sql, job_config=job_config)
+        rows = list(query_job.result())
+    except exceptions.NotFound as err:
+        print(
+            f"error: Cloud Bigtable table '{bigtable_table_id}' in instance "
+            f"'{bigtable_instance_id}' not found for project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+    except exceptions.GoogleAPICallError as err:
+        print(
+            f"error: failed to query Cloud Bigtable table '{bigtable_table_id}' in "
+            f"instance '{bigtable_instance_id}' for project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+
+    print(f"Resource ID: {source_uri}")
+    print(f"Job ID: {query_job.job_id}")
+    print(f"Rows Returned: {len(rows)}")
+    print(f"Temporary Table: {temp_table_name}")
+
+
+# [END bigquery_query_external_bigtable]

bigquery/biglake/bigquery_query_external_bigtable_test.py

@@ -0,0 +1,77 @@
+# 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_query_external_bigtable
+from google.api_core import exceptions
+import pytest
+
+
+def test_query_external_bigtable_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_row = mock.MagicMock()
+    mock_row.rowkey = "row-001"
+    mock_job.result.return_value = [mock_row]
+    mock_client.query.return_value = mock_job
+    monkeypatch.setattr(
+        bigquery_query_external_bigtable.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_query_external_bigtable.query_external_bigtable(
+        project_id="example-project",
+        bigtable_instance_id="example-bt-instance",
+        bigtable_table_id="example_bt_table",
+    )
+
+    captured = capsys.readouterr()
+    assert (
+        "Resource ID: https://googleapis.com/bigtable/projects/example-project"
+        in captured.out
+    )
+    assert "Rows Returned: 1" in captured.out
+    assert "Temporary Table: example_bigtable_temp" in captured.out
+    assert mock_client.query.called
+
+
+def test_query_external_bigtable_error(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    mock_client = mock.MagicMock()
+    mock_job = mock.MagicMock()
+    mock_job.result.side_effect = exceptions.NotFound("resource error")
+    mock_client.query.return_value = mock_job
+    monkeypatch.setattr(
+        bigquery_query_external_bigtable.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_query_external_bigtable.query_external_bigtable(
+        project_id="example-project",
+        bigtable_instance_id="example-bt-instance",
+        bigtable_table_id="example_bt_table",
+    )
+
+    captured = capsys.readouterr()
+    assert "error:" in captured.err
+    assert "example-bt-instance" in captured.err

bigquery/biglake/noxfile_config.py

@@ -0,0 +1,23 @@
+# 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.
+
+TEST_CONFIG_OVERRIDE = {
+    # You can opt out from the test for specific Python versions.
+    "ignored_versions": ["2.7", "3.7", "3.8", "3.9", "3.10", "3.11"],
+    # Enforce type hints on new samples.
+    "enforce_type_hints": True,
+    "gcloud_project_env": "GOOGLE_CLOUD_PROJECT",
+    "pip_version_override": None,
+    "envs": {},
+}

bigquery/biglake/requirements-test.txt

@@ -0,0 +1 @@
+pytest==9.0.3; python_version >= "3.10"

bigquery/biglake/requirements.txt

@@ -0,0 +1,2 @@
+google-cloud-bigquery==3.47.0
+google-cloud-bigquery-storage==2.43.0