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https://issues.apache.org/jira/browse/DERBY-6882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15220879#comment-15220879
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Rick Hillegas commented on DERBY-6882:
--------------------------------------
This seems like a useful enhancement. The Standard syntax is as Aleksei
indicates except that the trailing [AS IDENTITY] is not permitted. So
ALTER TABLE table1 ALTER COLUMN col1 SET GENERATED {ALWAYS | BY DEFAULT}
See part 2 of the 2011 SQL Standard, section 11.20 (<alter identity column
specification>).
> Add functionality to ALTER TABLE: switch from GENERATED ALWAYS to GENERATED
> BY DEFAULT
> --------------------------------------------------------------------------------------
>
> Key: DERBY-6882
> URL: https://issues.apache.org/jira/browse/DERBY-6882
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.12.1.1
> Reporter: Aleksei Kovura
> Labels: features
>
> I'm trying to import data from another Derby database with foreignViews tool
> because system tables got corrupted somehow (see
> https://issues.apache.org/jira/browse/DERBY-6876). Tables contain generated
> ID columns (created as "GENERATED ALWAYS"). Importing data and allowing Derby
> to generate new IDs in generated columns will break relationships between
> tables (old tables have counter gaps there due to deletes - IDs won't match).
> For a clean import without breaking DDL information in DB version control I
> would like to be able to switch between generated types as follows:
>
> ALTER TABLE table1 ALTER COLUMN col1 SET GENERATED BY DEFAULT [ AS IDENTITY]
> ALTER TABLE table1 ALTER COLUMN col1 SET GENERATED ALWAYS [ AS IDENTITY]
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