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Date: Sun, 10 Sep 2006 12:59:29 -0700 (PDT)
From: "Bryan Pendleton (JIRA)" <derby-dev@db.apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-1489) Provide ALTER TABLE DROP COLUMN
 functionality
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    [ http://issues.apache.org/jira/browse/DERBY-1489?page=comments#action_12433730 ] 
            
Bryan Pendleton commented on DERBY-1489:
----------------------------------------

I investigated the dependency manager to see how it handles column
permissions. It doesn't appear to track dependencies between column
permissions and the underlying columns. I sent a message to the derby-dev
list to inquire about this part of the GRANT implementation.

I've been studying how DROP COLUMN handles triggers which mention this
column, to see if that holds some clues for how to handle GRANTs which
mention this column. DROP COLUMN locates such triggers by asking the
DataDictionary for a list of all triggers on this table, then iterates through the
list, asking each trigger which columns it references, and then either cascades
the DROP to the affected trigger or fails the DROP, depending on whether the
user said CASCADE or RESTRICT.

Unfortunately, there don't appear to be analogous methods for column
permissions in the data dictionary to allow retrieval of all the column permissions
on this table, for example. 

So, for now, I don't have a way to handle GRANTed column permissions when
dropping a column from a table, and this appears to be a blocker problem
for this feature.


> Provide ALTER TABLE DROP COLUMN functionality
> ---------------------------------------------
>
>                 Key: DERBY-1489
>                 URL: http://issues.apache.org/jira/browse/DERBY-1489
>             Project: Derby
>          Issue Type: New Feature
>          Components: Documentation, SQL
>    Affects Versions: 10.1.3.1, 10.1.3.0, 10.1.2.1, 10.1.1.0, 10.0.2.1, 10.0.2.0, 10.2.1.0
>            Reporter: Bryan Pendleton
>         Assigned To: Bryan Pendleton
>         Attachments: dropColumn_2.diff, dropColumn_v3_view_drop.diff, dropColumn_v4_grant_tests.diff
>
>
> Provide a way to drop a column from an existing table. Possible syntax would be:
>   ALTER TABLE tablename DROP COLUMN columnname CASCADE / RESTRICT;
> Feature should properly handle columns which are used in constraints, views, triggers, indexes, etc.

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