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From "Deepa Remesh (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-119) Add ALTER TABLE option to change column from NULL to NOT NULL
Date Tue, 15 Aug 2006 00:19:16 GMT
    [ http://issues.apache.org/jira/browse/DERBY-119?page=comments#action_12427996 ] 
Deepa Remesh commented on DERBY-119:

Thanks Bryan for the updated patch. I read through the patch. It addresses my previous comments
and looks good to me. For your question:
Reviewers: do you think it would be better to create an entirely
new message to cover the UNIQUE case, rather than extending the
existing message to cover the additional case?

In my opinion, it is okay to re-use the same message as this message is used only once in
the code. So changing the message text shouldn't affect any other scenario. Also, I think
it is good to re-use messages where possible as this would help keep the jar size down.  

One small comment: Along with changing the message text, it may be good to change the name
of the SQLState variable "LANG_MODIFY_COLUMN_PKEY_CONSTRAINT" to indicate it also covers UNIQUE

> 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, alterColumnNotNull_v2.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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