Question

如果表存在，我有以下查询，但如果不存在则会出错。

WITH allTables AS ( 
  SELECT 
    CONCAT(user_dim.app_info.app_id, ':', user_dim.app_info.app_platform) as app,
    user_dim.app_info.app_instance_id AS users
  FROM `table.app_events_intraday_*`, UNNEST(event_dim) AS event
  WHERE _TABLE_SUFFIX BETWEEN '20170406' AND '20170406'

  UNION ALL
  SELECT 
    CONCAT(user_dim.app_info.app_id, ':', user_dim.app_info.app_platform) as app,
    user_dim.app_info.app_instance_id AS users
  FROM `table.app_events_*`, UNNEST(event_dim) AS event
  WHERE _TABLE_SUFFIX BETWEEN '20170406' AND '20170406'
) 
SELECT 
  app as target,
  COUNT(DISTINCT(users)) AS datapoint_value,
  UNIX_SECONDS(PARSE_TIMESTAMP('%Y%m%d', '20170406')) as datapoint_time
FROM allTables
GROUP BY app

此查询根据_TABLE_SUFFIX选择当前日期/时间范围活动用户。问题是当表不存在时，它会返回以下错误：

错误：项目：table.app_events_intraday_ *与任何表格都不匹配。

我知道这样做是因为该表不存在。我需要找到一种方法来检查表是否存在，然后再查询它。任何帮助都会很棒，谢谢！

Answer 1

尝试以下

#standardSQL
WITH allTables AS ( 
  SELECT 
    CONCAT(user_dim.app_info.app_id, ':', user_dim.app_info.app_platform) AS app,
    user_dim.app_info.app_instance_id AS users
  FROM `table.app_events_*`, UNNEST(event_dim) AS event
  WHERE _TABLE_SUFFIX BETWEEN 'intraday_20170406' AND 'intraday_20170406'

  UNION ALL
  SELECT 
    CONCAT(user_dim.app_info.app_id, ':', user_dim.app_info.app_platform) AS app,
    user_dim.app_info.app_instance_id AS users
  FROM `table.app_events_*`, UNNEST(event_dim) AS event
  WHERE _TABLE_SUFFIX BETWEEN '20170406' AND '20170406'
) 
SELECT 
  app AS target,
  COUNT(DISTINCT(users)) AS datapoint_value,
  UNIX_SECONDS(PARSE_TIMESTAMP('%Y%m%d', '20170406')) AS datapoint_time
FROM allTables
GROUP BY app

或者它可以＆＃34;重构＆＃34;进入

#standardSQL
WITH allTables AS ( 
  SELECT 
    CONCAT(user_dim.app_info.app_id, ':', user_dim.app_info.app_platform) AS app,
    user_dim.app_info.app_instance_id AS users
  FROM `table.app_events_*`, UNNEST(event_dim) AS event
  WHERE _TABLE_SUFFIX BETWEEN '20170406' AND '20170406'
  OR _TABLE_SUFFIX BETWEEN 'intraday_20170406' AND 'intraday_20170406'
) 
SELECT 
  app AS target,
  COUNT(DISTINCT(users)) AS datapoint_value,
  UNIX_SECONDS(PARSE_TIMESTAMP('%Y%m%d', '20170406')) AS datapoint_time
FROM allTables
GROUP BY app

Answer 2

我建议添加名为app_events_intraday_empty的空表，其格式与真实表相同，这样即使实际表不存在，您的查询也不会出错

Answer 3

检查表是否存在的一种方法（还有更多）（在dbo模式上）：

IF EXISTS (SELECT 1 FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[YourTableName]') AND [type] in (N'U'))
Begin
--DoSomething
End

在运行查询之前检查这些表是否存在，并根据结果返回不同的数据？

3 个答案: