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Date: Tue, 7 Nov 2006 14:56:55 -0800 (PST)
From: "Bryan Pendleton (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-1515) Provide ALTER TABLE functionality to
 change a column's data type
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    [ http://issues.apache.org/jira/browse/DERBY-1515?page=comments#action_12447952 ] 
            
Bryan Pendleton commented on DERBY-1515:
----------------------------------------

Knut Anders pointed out that it isn't necessary to rename column c1 to c1_oldtype.
The technique can be simplified to:

1) ALTER TABLE t ADD COLUMN c1_newtype NEWTYPE;
2) UPDATE t SET c1_newtype = c1;
3) ALTER TABLE t DROP COLUMN c1;
4) ALTER TABLE t RENAME COLUMN c1_newtype to c1;


> Provide ALTER TABLE functionality to change a column's data type
> ----------------------------------------------------------------
>
>                 Key: DERBY-1515
>                 URL: http://issues.apache.org/jira/browse/DERBY-1515
>             Project: Derby
>          Issue Type: New Feature
>          Components: Documentation, SQL
>    Affects Versions: 10.1.1.0, 10.2.1.6, 10.1.2.1, 10.1.3.1
>            Reporter: Bryan Pendleton
>            Priority: Minor
>
> Derby should provide a feature which allows a user to change the data type of an existing column in an existing table.
> Currently, there exists the statement:
>     ALTER TABLE tablename ALTER COLUMN columnname SET DATA TYPE datatype
> However, this statement currently only allows increasing the length of a VARCHAR column. You are not allowed to decrease the width or to change the data type.
> It would be nice if this restriction could be lifted, and the datatype could be changed.

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