> The table had another rows before, but I had deleted them and commited. I
> had added new rows and commited.
>
> That can be the problem?

My test was with existing records, so if you have declared the third
field as NOT NULL, committed this change, inserted values into this new
field, committed that as well, then the new primary key constraint
should work fine.

Are you the only one connected to the database when doing this change?

> By the way, I'm using version 2.5

My test ran with 2.1.4 and 2.5.0 just fine.


--
With regards,

Thomas Steinmaurer
Upscene Productions
http://www.upscene.com
http://blog.upscene.com/thomas/

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