要将一个Firestore集合与其子集合进行连接，您可以使用BigQuery的标准SQL语法来编写查询。下面是一个示例代码，演示了如何连接Firestore集合和其子集合：

from google.cloud import bigquery
from google.cloud.firestore_v1 import ArrayUnion, ArrayRemove

# 创建一个BigQuery客户端
client = bigquery.Client()

# 定义Firestore集合的名称
collection_name = 'your_collection_name'
subcollection_name = 'your_subcollection_name'

# 定义BigQuery数据集和表的名称
dataset_name = 'your_dataset_name'
table_name = 'your_table_name'

# 创建一个BigQuery表
table_ref = client.dataset(dataset_name).table(table_name)
schema = [
    bigquery.SchemaField('collection_name', 'STRING'),
    bigquery.SchemaField('subcollection_name', 'STRING'),
    bigquery.SchemaField('document_id', 'STRING'),
    bigquery.SchemaField('field1', 'STRING'),
    bigquery.SchemaField('field2', 'INTEGER')
]
table = bigquery.Table(table_ref, schema=schema)
table = client.create_table(table)

# 查询Firestore集合
query = f"""
    SELECT
      '{collection_name}' AS collection_name,
      NULL AS subcollection_name,
      document_id,
      field1,
      field2
    FROM
      `your_project.your_firestore_dataset.{collection_name}`
"""
query_job = client.query(query)
results = query_job.result()

# 将Firestore集合的结果写入BigQuery表
rows_to_insert = []
for row in results:
    rows_to_insert.append((
        row.collection_name,
        row.subcollection_name,
        row.document_id,
        row.field1,
        row.field2
    ))
client.insert_rows(table, rows_to_insert)

# 查询Firestore子集合
query = f"""
    SELECT
      '{collection_name}' AS collection_name,
      '{subcollection_name}' AS subcollection_name,
      document_id,
      field1,
      field2
    FROM
      `your_project.your_firestore_dataset.{collection_name}.{subcollection_name}`
"""
query_job = client.query(query)
results = query_job.result()

# 将Firestore子集合的结果写入BigQuery表
rows_to_insert = []
for row in results:
    rows_to_insert.append((
        row.collection_name,
        row.subcollection_name,
        row.document_id,
        row.field1,
        row.field2
    ))
client.insert_rows(table, rows_to_insert)

请注意，您需要将代码中的以下变量替换为您自己的值：

• your_collection_name：Firestore集合的名称。
• your_subcollection_name：Firestore子集合的名称。
• your_dataset_name：BigQuery数据集的名称。
• your_table_name：BigQuery表的名称。
• your_project：您的Google Cloud项目的名称。

此代码示例会将Firestore集合和其子集合的数据写入到一个BigQuery表中。您可以根据自己的需求进行修改和扩展。