是否可以重新命名列？ [英] Is it possible to rename columns?

问题描述

是否有可能发布类似于

  RENAME COLUMN col1 col2 
  

在Google Cloud Spanner中？从DDL看来，这是不可能的;如果不是，这是一个设计选择还是限制，而在Beta？

解决方案

不，这是不可能的。目前，您只能对表中的列进行以下操作：

• 添加一个新的
  
• 
  
• 更改删除行为（级联或不行）


• 在 STRING 和 BYTES


• 更改 STRING的长度和 BYTES


• 添加或删除 NOT NULL 修饰符

按照以下步骤操作即可解决问题：

• 将新列添加到您的表中
  
• 更新您的代码以从两列读取
  
• 更新您的代码以仅写入新的
  
• 运行Cloud Dataflow作业将数据从旧列迁移到新列


• 更新您的代码以仅从新列


• 删除旧列

请记住，上述步骤对于t他是主键列，你必须通过创建一个新表来完成数据迁移。

Is it possible to issue something like

RENAME COLUMN col1 col2

in Google Cloud Spanner? It looks from the DDL that this isn't possible; if not, is this a design choice or a limitation whilst in Beta?

解决方案

No, this is not possible. Currently you can only do the following with regard to altering columns in a table:

• Add a new one
• Delete an existing one, unless it's a key column
• Change delete behavior (cascading or not)
• Convert between STRING and BYTES
• Change length of STRING and BYTES
• Add or remove NOT NULL modifier

A work around is possible by following these steps in order:

• Add the new column to your table
• Update your code to read to from both columns
• Update your code to only write to the new one
• Run a Cloud Dataflow job to migrate the data from the old column to the new column
• Update your code to only read from the new column
• Drop the old column

Keep in mind the above steps will not work for the primary key column, you'll have to do by creating a new table, and doing the data migration that way.

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