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From "Bryan Pendleton (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-119) Add ALTER TABLE option to change column from NULL to NOT NULL
Date Mon, 31 Jul 2006 21:02:19 GMT
    [ http://issues.apache.org/jira/browse/DERBY-119?page=comments#action_12424654 ] 
            
Bryan Pendleton commented on DERBY-119:
---------------------------------------

I believe the patch completes the future, sorry for the confusing comment. I believe that
the existing execution code in AlterTableConstantAction.java is fine as is, and so this new
feature just requires parser changes and tests. When I apply the patch in my environment,
the feature seems to be working fine.

I suspect that I haven't added enough tests, so suggestions and feedback about how to write
more tests would be helpful; I don't have a lot of experience writing tests in this area.


> Add ALTER TABLE option to change column from NULL to NOT NULL
> -------------------------------------------------------------
>
>                 Key: DERBY-119
>                 URL: http://issues.apache.org/jira/browse/DERBY-119
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Bernd Ruehlicke
>         Assigned To: Bryan Pendleton
>         Attachments: alterColumnNotNull_1.diff
>
>
> There was a thread about this on the Cloudscape forum
> http://www-106.ibm.com/developerworks/forums/dw_thread.jsp?message=4103269&cat=19&thread=59941&forum=370#4103269
> Since this describes the problem I will just copy the content of this entry as my dexscription
> The content of this was 
> "
> Hi,
> I stumbled across a behaviour of cloudscape which is not a bug but IMHO an implementation
choice. To assign a primary key to a table using ALTER TABLE all columns must be declared
NOT NULL first, which can only be specified upon column creation (no ALTER TABLE statement
exists to change the NOT NULL property of a column).
> Most databases I know do two things differently:
> 1) when a primary key is assigned all pk columns are automatically set to NOT NULL, if
one of them contains NULL values, the ALTER TABLE statement fails
> 2) it is possible to alter the column to set the NOT NULL property after column creation
(fails when there are already records containing NULL values)
> If I have understood the limitations correctly in Cloudscape I have no choice but to
remove and re-add the column which is supposed to be used in the primary key, if it is not
already declared as NOT NULL. This means that in the case of a table containing valid data
(unique and not null) in the column in all records, I would have to export the data, remove
and re-add the column and reimport that data, which would not be necessary e.g. in Oracle
or MaxDB.
> Is it possible to change that behaviour or is there a good reason for it? It looks as
if it makes the life of the user more difficult than necessary for certain metadata manipulations.
Making it possible to alter the NOT NULL property of a column would solve this and IMHO having
a primary key constraint do this implicitly makes sense as well. 
> Thanks in advance for any insight on this,
> Robert"

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