SQL 将 yyyymmdd 转换为 BigQuery 中的时间戳？

Question

我试图在 SQL 中将字符串转换为时间戳。问题其实很简单，如何将这个字符串转换成当天午夜开始的时间戳？

在我的数据库中，我还在 timestamp_micros 中存储了一个字段，其中任何一个都可以工作，我认为将 micros 转换为时间戳比字符串更容易。

例如 20170118 => 时间戳

查询:

WITH allTables as (
  SELECT
      event.date as date,
      count(*) as totalSessions,
      count(DISTINCT user_dim.app_info.app_instance_id) as uniqueUsers
  FROM `namehiddenonlyhere.*`
  CROSS JOIN
      UNNEST(event_dim) AS event
  WHERE
      event.name = 'session_start'
  AND 
      event.date <= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 1 DAY))
  AND
      event.date >= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 7 DAY))
  GROUP BY event.date

  UNION ALL 
  SELECT
      event.date as date,
      count(*) as totalSessions,
      count(DISTINCT user_dim.app_info.app_instance_id) as uniqueUsers
  FROM `namehiddenonlyhere.*`
  CROSS JOIN
      UNNEST(event_dim) AS event
  WHERE
      event.name = 'session_start'
  AND 
      event.date <= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 1 DAY))
  AND
      event.date >= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 7 DAY))
  GROUP BY event.date
) SELECT 'all apps' as target, date as datapoint_time, totalSessions datapoint_value FROM allTables;

Answer 1

您可以使用 PARSE_DATE 或 PARSE_TIMESTAMP(格式字符串相同)来获取日期或时间戳。例如:

SELECT
  d,
  PARSE_DATE('%Y%m%d', d) AS date,
  PARSE_TIMESTAMP('%Y%m%d', d) AS timestamp
FROM UNNEST(['20170117', '20161231']) AS d;

您可以在文档中阅读有关格式字符串的更多信息。有 date 的部分和 timestamp ，分别适用于 PARSE_DATE 和 PARSE_TIMESTAMP。

编辑:根据您更新的问题，您可以将查询更改为如下内容:

WITH allTables as (
  SELECT
      event.date as date,
      count(*) as totalSessions,
      count(DISTINCT user_dim.app_info.app_instance_id) as uniqueUsers
  FROM `namehiddenonlyhere.*`
  CROSS JOIN
      UNNEST(event_dim) AS event
  WHERE
      event.name = 'session_start'
  AND 
      event.date <= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 1 DAY))
  AND
      event.date >= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 7 DAY))
  GROUP BY event.date

  UNION ALL 
  SELECT
      event.date as date,
      count(*) as totalSessions,
      count(DISTINCT user_dim.app_info.app_instance_id) as uniqueUsers
  FROM `namehiddenonlyhere.*`
  CROSS JOIN
      UNNEST(event_dim) AS event
  WHERE
      event.name = 'session_start'
  AND 
      event.date <= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 1 DAY))
  AND
      event.date >= FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE, INTERVAL 7 DAY))
  GROUP BY event.date
) SELECT 'all apps' as target, PARSE_DATE('%Y%m%d', date) as datapoint_time, totalSessions datapoint_value FROM allTables;

我所做的唯一修改是更改:

date AS datapoint_time

到:

PARSE_DATE('%Y%m%d', date) as datapoint_time