Oracle FAQ Your Portal to the Oracle Knowledge Grid

Home -> Community -> Mailing Lists -> Oracle-L -> Re: Drop unused Column

Re: Drop unused Column

From: Ken Payton <>
Date: Thu, 04 Aug 2005 13:24:45 -0400
Message-Id: <>

Thanks Dennis,

The DBA was dropping a column that was already marked unused previously, hence the drop unused column statement. The problem was the drop, which was necessary, was underestimated.

Thanks Deepak,

Recreating the table and recreating the indexes could take a couple weeks on an idle system. We actually have several tables that we have to address, just plan to do so with a different approach.

Here are a few notes I thought I would share with the group.

Using the drop unused column command is an online action, although you need to watch out for rollback.

Using the drop unused column checkpoint option blocks queries.

Killing the session issuing the drop unused column with checkpoint renders the table useless to online apps. The only options are truncate table, drop table or drop unused columns continue, which still renders the table inaccessible.

A nifty little bug we found in doing some of our research is that transportable tablespaces do not recognize unused columns and exports the DDL without the unused columns. Unfortunately this shifts the trailing columns, misaligning data or causing errors if data type mismatches occur due to the new alignment.


On Thu, 2005-08-04 at 10:22, Dennis Williams wrote:
> Ken,
> My guess is that the Oracle kernel is slogging away. You could bounce
> the instance, but you might end up wrecking something worse. I think
> the moral to the story is to be extremely careful what commands you
> issue in production and any command you aren't entirely comfortable
> with, issue it on test first. Another alternative would have been to
> issue the "set unused" parameter on this command. Hang in there.
> Dennis Williams
> On 8/3/05, Ken Payton <> wrote:
> It's gone, in fact the DBA has issued the the alter table drop
> columns
> continue command. It is currently running. Unfortunately,
> the table is
> not accessible during this time.

Kenny Payton
Software Architect
Public Records Group
Choicepoint, Inc.
o: (770)752-4054

The information contained in this e-mail message is intended only for
the personal and confidential use of the recipient(s) named above. This
message may be an attorney-client communication and/or work product and
as such is privileged and confidential. If the reader of this message
is not the intended recipient or an agent responsible for delivering it
to the intended recipient, you are hereby notified that you have
received this document in error and that any review, dissemination,
distribution, or copying of this message is strictly prohibited. If you
have received this communication in error, please notify us immediately
by e-mail, and delete the original message.

Received on Thu Aug 04 2005 - 12:27:30 CDT

Original text of this message