feat(bigquery): add bigquery_create_vector_index_tree_ah sample to create a TreeAH vector index on embedding column

Problem:
The BigQuery documentation (https://cloud.google.com/bigquery/docs/vector-index)
needs a standalone, tested Python code sample demonstrating how to
create a TreeAH vector index on embedding column (region tag `bigquery_create_vector_index_tree_ah`).

Solution:
- Add `create_vector_index_tree_ah(project_id: str, dataset_id: str, table_id: str) -> None` in `bigquery/vector_search/bigquery_create_vector_index_tree_ah.py`
  (Create a ScaNN-based TREE_AH vector index on an embedding column in BigQuery using CREATE OR REPLACE VECTOR INDEX.)
- Add unit tests (`bigquery/vector_search/bigquery_create_vector_index_tree_ah_test.py`) covering both the success
  path and API error handling (`GoogleAPICallError`)

Author: iennae

bigquery/vector_search/bigquery_create_vector_index_tree_ah.py

@@ -0,0 +1,76 @@
+# 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_create_vector_index_tree_ah]
+import sys
+
+from google.api_core import exceptions
+from google.cloud import bigquery
+
+
+def create_vector_index_tree_ah(
+    project_id: str,
+    dataset_id: str,
+    table_id: str,
+) -> None:
+    """Creates a TreeAH vector index on an embedding column in a BigQuery table.
+
+    Args:
+        project_id: Google Cloud project ID (for example, 'example-project').
+        dataset_id: BigQuery dataset ID containing the target table
+            (for example, 'example_dataset').
+        table_id: BigQuery table ID containing the embedding column
+            (for example, 'example_embeddings').
+    """
+    client = bigquery.Client(project=project_id)
+    index_name = "example_tree_ah_index"
+    table_ref = f"{project_id}.{dataset_id}.{table_id}"
+    # TreeAH indexes use asymmetric hashing optimized for batch and single-query vector search.
+    sql = f"""
+        CREATE OR REPLACE VECTOR INDEX `{index_name}`
+        ON `{table_ref}`(embedding)
+        OPTIONS(
+          index_type = 'TREE_AH',
+          distance_type = 'COSINE',
+          tree_ah_options = '{{"normalization_type": "L2"}}'
+        );
+    """
+
+    try:
+        print(f"Creating TreeAH vector index {index_name} on table: {table_ref}")
+        query_job = client.query(sql)
+        query_job.result()
+    except exceptions.NotFound as err:
+        print(
+            f"error: table '{table_id}' or dataset '{dataset_id}' not found in "
+            f"project '{project_id}' when creating index '{index_name}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+    except exceptions.GoogleAPICallError as err:
+        print(
+            f"error: failed to create TreeAH vector index '{index_name}' on table "
+            f"'{table_id}' in dataset '{dataset_id}' for project '{project_id}': {err.message}",
+            file=sys.stderr,
+        )
+        return
+
+    print(f"Resource ID: {table_ref}")
+    print(f"Index Name: {index_name}")
+    print("Index Type: TREE_AH")
+    print(f"Job ID: {query_job.job_id}")
+    print(f"Statement Type: {query_job.statement_type}")
+
+
+# [END bigquery_create_vector_index_tree_ah]

bigquery/vector_search/bigquery_create_vector_index_tree_ah_test.py

@@ -0,0 +1,73 @@
+# 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_create_vector_index_tree_ah
+from google.api_core import exceptions
+import pytest
+
+
+def test_create_vector_index_tree_ah_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.statement_type = "CREATE_VECTOR_INDEX"
+    mock_client.query.return_value = mock_job
+    monkeypatch.setattr(
+        bigquery_create_vector_index_tree_ah.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_create_vector_index_tree_ah.create_vector_index_tree_ah(
+        project_id="example-project",
+        dataset_id="example_dataset",
+        table_id="example_embeddings",
+    )
+
+    captured = capsys.readouterr()
+    assert (
+        "Resource ID: example-project.example_dataset.example_embeddings"
+        in captured.out
+    )
+    assert "Index Name: example_tree_ah_index" in captured.out
+    assert "Index Type: TREE_AH" in captured.out
+    assert mock_client.query.called
+
+
+def test_create_vector_index_tree_ah_error(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    mock_client = mock.MagicMock()
+    mock_client.query.side_effect = exceptions.NotFound("ddl error")
+    monkeypatch.setattr(
+        bigquery_create_vector_index_tree_ah.bigquery,
+        "Client",
+        lambda project=None: mock_client,
+    )
+
+    bigquery_create_vector_index_tree_ah.create_vector_index_tree_ah(
+        project_id="example-project",
+        dataset_id="example_dataset",
+        table_id="example_embeddings",
+    )
+
+    captured = capsys.readouterr()
+    assert "error:" in captured.err
+    assert "example_tree_ah_index" in captured.err

bigquery/vector_search/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/vector_search/requirements-test.txt

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

bigquery/vector_search/requirements.txt

@@ -0,0 +1 @@
+google-cloud-bigquery==3.47.0