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From "Rick Hillegas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5493) Same value returned by successive calls to a sequence generator.
Date Thu, 12 Apr 2012 19:11:17 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252750#comment-13252750
] 

Rick Hillegas commented on DERBY-5493:
--------------------------------------

I don't think that there is any wiggle room in the Standard, but I also think that the correctness
problem with identity columns is not one that most users are going to care about. As you say,
users are most likely going to be interested in never seeing duplicates in primary key columns.
The only edge case I can think of is an application which was coded before we introduced sequences
and which created a table with one column, an identity column, used to simulate a unique id
generator for the whole application. That edge case would be concerned about the correctness
problem with identity columns. Thanks.
                
> Same value returned by successive calls to a sequence generator.
> ----------------------------------------------------------------
>
>                 Key: DERBY-5493
>                 URL: https://issues.apache.org/jira/browse/DERBY-5493
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.6.1.0, 10.6.2.1, 10.7.1.1, 10.8.1.2, 10.8.2.2, 10.9.0.0
>            Reporter: Rick Hillegas
>            Assignee: Rick Hillegas
>              Labels: derby_triage10_9
>         Attachments: derby-5493-01-aa-correctnessPlusPeekerPlusTest.diff, derby-5493-01-ad-simplerApproach.diff,
derby-5493-01-ae-simplerApproachWithCrashJUnitTest.diff
>
>
> The following script shows the same value being returned from a sequence generator by
two successive NEXT VALUE FOR calls. Thanks to Knut for finding this:
> connect 'jdbc:derby:memory:db;create=true';
> create table t (x int);
> create sequence s;
> autocommit off;
> select count(*) from sys.syssequences with rs;
> values next value for s;
> drop table t;
> rollback;
> -- same value as previous call
> values next value for s; 

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