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From "Jacques Le Roux" <jacques.le.r...@les7arts.com>
Subject Re: Exception occured when I try to add a new person
Date Thu, 05 May 2011 09:10:45 GMT
Yes indeed this is know reason and why we have use-indices-unique="false" by default for Derby
see http://svn.apache.org/viewvc?view=revision&revision=544640

I have completed r544640 by adding an explicit comment about use-indices-unique="false" at


From: "Leon2" <sun.hao@labwayit.com>
>I found the cause. It's because that Derby treats "null" as a normal value in
> its unique indice implementation. If you create an unique index, derby will
> set the unique constraint on whole combination of all index fields no matter
> the value of one field is null or not.
> e.g. table 'test' has two columns (a int not null, b int) with unique index
> on (a, b), then value combination (1, null) can be inserted into table once
> and only once.
> Workaround:  set use-indices-unique="false" explicitly in entityengine.xml
> for derby database.
> to Jacques,
> Not test it on Postgres yet, but I think Postgres should be ok since
> Postgres doesn't allow nullable column in unique indice. That means (1,
> null) can be inserted to test table twice without unique index violation in
> previous example.
> to adnane,
> That's great. I need such detail document. I'm evaluating the feasibility to
> migrate the mysql database to postgres. The most important reason is
> Timestamp type of mysql does not support milliseconds. So, thank you in
> advance ^^.  You can send it to 'sun.hao' at 'labwayit' dot 'com'.
> --
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