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From "Danoja Dias (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6852) Allow identity columns to cycle (as defined in SQL:2003)
Date Thu, 16 Jun 2016 06:35:05 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15333210#comment-15333210
] 

Danoja Dias commented on DERBY-6852:
------------------------------------

Hi Bryan,

According to What I have understand about the cycle option, 

When the value is overflowed, it must start with the minimum value. I think It is the process
defined in SQL:2003. 
For example when identity is given as follows, 
    a int generated always as identity ( start with 100 )

When a is overflowed, I thought it should start from minimum value, not from 100. 

Have I misunderstood the process?

Thanks. 

> Allow identity columns to cycle (as defined in SQL:2003)
> --------------------------------------------------------
>
>                 Key: DERBY-6852
>                 URL: https://issues.apache.org/jira/browse/DERBY-6852
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Peter Hansson
>
> Currently when an IDENTITY column reaches its maximum value it will produce an error.
> For tables that are used as 'transaction logs' or 'event logs' it often makes sense to
let the table automatically start over with the first identity value again when the max is
reached. This would be similar to the CYCLE option on Oracle's SEQUENCE and as defined in
SQL:2003. And Derby is probably used quite often for this purpose, I guess, perhaps even more
than other RDBMSs.
> At the moment every developer have to program their own logic for this.
> I propose to introduce the CYCLE option.
> The idea of CYCLE is based on the assumption that there's been a prior cleanup in the
table rows so that it will be possible to re-use ids that have been used previously. If that
is not the case - and a rollover happens - then a duplicate value error will occur. In this
sense it can be argued that the CYCLE option will trade a _certain_ error for a _potential_
error. Most Derby users would possibly gladly accept such a bargain. In other words: This
option will greatly enhance the usability of IDENTITY columns.
> The current implementation of IDENTITY columns SQL grammar in Derby is a subset of the
SQL:2003 standard which is the first of the SQL standards to define IDENTITY columns. Interestingly
the standard also defines the CYCLE option but this was never implemented in Derby. Also see
[SQL-99 and SQL-2003 features mapped to Derby|https://wiki.apache.org/db-derby/SQLvsDerbyFeatures]
(scroll to T174).
> In other words: The proposal is simply to implement CYCLE as defined in SQL:2003.



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