Add ALTER TABLE option to change column from NULL to NOT NULL
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Key: DERBY-119
URL: http://issues.apache.org/jira/browse/DERBY-119
Project: Derby
Type: New Feature
Reporter: Bernd Ruehlicke
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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