BigQuery 检查表是否存在 [英] BigQuery check if table exists or not

问题描述

我正在使用 C# 根据来自 bigquery api 表端点的响应动态构建查询.我正在尝试计算有效的活跃用户，但前提是我选择每个带有 .* 的表.我的问题真的很简单，有没有办法检查 BigQuery SQL 中是否存在表?

I'm using C# to dynamically construct a query based on a response from the bigquery api tables endpoint. I'm trying to calculate active users which works, but only if I select every table with .*. My question is quite simple really, is there a way to check if a table exists within BigQuery SQL?

推荐答案

有名为 __TABLES__ 和 __TABLES_SUMMARY__

您可以运行如下查询:

SELECT size_bytes FROM <dataset>.__TABLES__ WHERE table_id='mytablename'

该查询的 __TABLES__ 部分可能看起来不熟悉.__TABLES_SUMMARY__ 是一个元表，包含有关数据集中表的信息.你可以自己使用这个元表.例如，查询 SELECT * FROM publicdata:samples.__TABLES_SUMMARY__ 将返回有关 publicdata:samples 数据集中表的元数据.你也可以做 SELECT * FROM publicdata:samples.__TABLES__

The __TABLES__ portion of that query may look unfamiliar. __TABLES_SUMMARY__ is a meta-table containing information about tables in a dataset. You can use this meta-table yourself. For example, the query SELECT * FROM publicdata:samples.__TABLES_SUMMARY__ will return metadata about the tables in the publicdata:samples dataset. You can also do SELECT * FROM publicdata:samples.__TABLES__

可用字段:

__TABLES_SUMMARY__ 元表的字段(在 TABLE_QUERY 查询中都可用)包括:

The fields of the __TABLES_SUMMARY__ meta-table (that are all available in the TABLE_QUERY query) include:

• table_id:表名.
• creation_time:创建表的时间，以 UTC 时间 1/1/1970 以来的毫秒数为单位.这与表中的 creation_time 字段相同.
• type:是视图(2)还是普通表(1).

• table_id: name of the table.
• creation_time: time, in milliseconds since 1/1/1970 UTC, that the table was created. This is the same as the creation_time field on the table.
• type: whether it is a view (2) or regular table (1).

以下字段在 TABLE_QUERY() 中不可用，因为它们是 __TABLES__ 的成员，但不是 __TABLES_SUMMARY__.它们被保留在这里是为了历史兴趣并部分记录 __TABLES__ 元表:

The following fields are not available in TABLE_QUERY() since they are members of __TABLES__ but not __TABLES_SUMMARY__. They're kept here for historical interest and to partially document the __TABLES__ metatable:

• last_modified_time:时间，自 1970 年 1 月 1 日 UTC 起更新表(元数据或表内容)的毫秒数.请注意，如果您使用 tabledata.insertAll() 将记录流式传输到您的表，这可能会过时几分钟.
• row_count:表中的行数.
• size_bytes:表的总大小(以字节为单位).

• last_modified_time: time, in milliseconds since 1/1/1970 UTC, that the table was updated (either metadata or table contents). Note that if you use the tabledata.insertAll() to stream records to your table, this might be a few minutes out of date.
• row_count: number of rows in the table.
• size_bytes: total size in bytes of the table.

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