Ниже приведен пример для BigQuery Standard SQL
#standardSQL
WITH `project.dataset.table` AS (
SELECT 'Fri, 31 Aug 2018 13:00:57 +0000' ts_string
)
SELECT
ts_string,
PARSE_TIMESTAMP('%a, %d %b %Y %X %z' , ts_string) ts_timestamp,
DATETIME(PARSE_TIMESTAMP('%a, %d %b %Y %X %z' , ts_string)) ts_datetime
FROM `project.dataset.table`
с результатом
Row ts_string ts_timestamp ts_datetime
1 Fri, 31 Aug 2018 13:00:57 +0000 2018-08-31 13:00:57 UTC 2018-08-31T13:00:57