如何从 BigQuery API 获取列名称？

Question

我可以使用以下代码获取列值：

os.environ['GOOGLE_APPLICATION_CREDENTIALS'] = 'C:\\Users\xxx\Desktop\key.json'
bq_client = Client()
query = "SELECT msts, coreuserid, spend_usd FROM `project.f_purchase` where dt = '2019-04-02' limit 5"
query_job = bq_client.query(query)
results = query_job.result()   

for row in results:
    print("{}, {}, {}".format(row.msts, row.uid, row.spend_amount))

但如最后一行所示，这需要直接列名。现在我有多个查询，我想运行它们并显示结果。有没有类似的方法.format(row.column1, row.column2...)？此外，查询的结果列数也不同。

任何帮助表示赞赏。

Answer 1

根据 BigQuery Python 客户端文档，您可以按如下方式循环行对象，而无需指定确切的列名称：

for row in query_job:  # API request - fetches results
    # Row values can be accessed by field name or index
    assert row[0] == row.name == row["name"]
    print(row)

此外，您始终可以使用此答案中所述的SchemaField 值

result = ["{0} {1}".format(schema.name,schema.field_type) for schema in table.schema]

这是一个使用 BigQuery 公共数据集来了解如何在不指定字段名称的情况下访问字段的示例：

from google.cloud import bigquery
from pprint import pprint
import json

client = bigquery.Client()

query = (
    "SELECT state,max(gender) as gender FROM `bigquery-public-data.usa_names.usa_1910_2013` "
    'GROUP BY state '
    "LIMIT 10"
)
query_job = client.query(
    query,
    # Location must match that of the dataset(s) referenced in the query.
    location="US",
)  # API request - starts the query

for num, row in enumerate(query_job, start=1):  # API request - fetches results
    # Row values can be accessed by field name or index
    # assert row[0] == row.name == row["name"]
    print("{} AS {}, {} AS {}".format(row[0], query_job._query_results._properties['schema']['fields'][0]['name'], row[1], query_job._query_results._properties['schema']['fields'][1]['name']))

    #print(row[0], row[1])

print(json.dumps(query_job._query_results._properties['schema']['fields'][0]['name']))
print(query_job._query_results._properties)
#pprint(vars(query_job._query_results._properties))

产生以下输出：

superQuery:bin tamirklein$ python test.py
AK AS state, M AS gender
AL AS state, M AS gender
AR AS state, M AS gender
AZ AS state, M AS gender
CA AS state, M AS gender
CO AS state, M AS gender
CT AS state, M AS gender
DC AS state, M AS gender
DE AS state, M AS gender
FL AS state, M AS gender

Answer 2

您还可以将 for 循环中的行转换为 dict （通过dict(row)）。那么键就是列名，你可以对字典做任何你能做的事情——迭代键（列名）、值（列值）或两者一起迭代，而不需要预先明确地知道列名。