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https://issues.apache.org/jira/browse/DERBY-6668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14064255#comment-14064255
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Rick Hillegas commented on DERBY-6668:
--------------------------------------
Note that even if the tables are empty, the TRUNCATE is not allowed on
10.10.2.0 (for the non-deferabble constraints allowed in that release). So
there should be no backward compatibility problem and no need for a release
note.
> Truncating a table may silently violate a deferred foreign key.
> ---------------------------------------------------------------
>
> Key: DERBY-6668
> URL: https://issues.apache.org/jira/browse/DERBY-6668
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.11.0.0
> Reporter: Rick Hillegas
> Assignee: Rick Hillegas
> Attachments: derby-6668-01-aa-disallowTruncateOnReferencedTable.diff
>
>
> If you truncate a table which is referenced by a deferred foreign key,
> orphaned tuples are left in the foreign table. That is, the foreign key is
> violated but no exception is raised.
> Since table truncation involves changing conglomerate ids, this may be
> another case of derby-6665. Or this may be a new bug.
> The following script shows this behavior:
> {noformat}
> connect 'jdbc:derby:memory:db;create=true';
> create table tunique
> (
> a int not null unique
> );
> create table tref
> (
> a int references tunique( a ) initially deferred
> );
> insert into tunique values ( 1 );
> insert into tref values ( 1 );
> truncate table tunique;
> -- the unique table is empty
> select * from tunique;
> -- but the table which references it has a row
> select * from tref;
> {noformat}
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