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Date: Wed, 20 Sep 2006 08:58:25 -0700 (PDT)
From: "Kristian Waagan (JIRA)" <derby-dev@db.apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-1495) Attempt to modify an identity column
 error after resetting identity column
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    [ http://issues.apache.org/jira/browse/DERBY-1495?page=3Dcomments#actio=
n_12436264 ]=20
           =20
Kristian Waagan commented on DERBY-1495:
----------------------------------------

Thanks Bryan.

I have been able to determine what seems to be causing the problem, but hav=
e not yet understood how to fix it. This is my first venture into the this =
area of the code, so things are very unclear to me.

First, after studying the various variables describing an identity column, =
I noticed that if the DefaultInfo assoiciated with an identity column is nu=
ll, the column is said to be "generated always as identity". In effect, the=
 column definition is changed after the restart/increment operation, becaus=
e the defaultInfo is set to null. This can be observed with the new describ=
e command in ij.

Bryan's guess seems to be valid, but if I add the old DefaultInfoImpl insta=
nce to the new one, I get a NPE when doing a drop on the table the next tim=
e I boot the database. It happens for 'BasicDependencyManager.clearDependen=
cies'. It also happens if I create a new instance (new DefaultInfoImpl(true=
,null,null)) and add it to the newly created ColumnDescriptor. This piece o=
f the code is in AlterTableConstantAction.modifyColumnDefault, as Bryan men=
tioned.

Is the error in this method, or does it happen earlier so the input is not =
as expected?
What step have I forgotten to do?

I'll keep looking into this, but any piece of further advice is appreciated=
!

> Attempt to modify an identity column error after resetting identity colum=
n
> -------------------------------------------------------------------------=
-
>
>                 Key: DERBY-1495
>                 URL: http://issues.apache.org/jira/browse/DERBY-1495
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.2.1.0
>         Environment: Java 1.5.0_06-b05 on Linux Ubuntu 5.10. Derby versio=
n 10.2.0.3-412239
>            Reporter: Lars Gr=C3=A5mark
>            Priority: Minor
>
> When an identity counter is altered using the ALTER TABLE statement below=
, it seems as if the GENERATED BY DEFAULT behavior is lost.
> The following statements will reproduce the error.
> CREATE TABLE MYTABLE (
>   id   INT GENERATED BY DEFAULT AS IDENTITY (START WITH 1, INCREMENT BY 1=
) NOT NULL
>  ,col2 INT NOT NULL
> )
> -- Insert using an explicit value on the ID-field
> INSERT INTO MYTABLE(ID, COL2) VALUES(2, 2)
> -- Reset the identity field
> ALTER TABLE mytable ALTER COLUMN id RESTART WITH 3
> -- Try inserting another explicit value and the error below is thrown.
> INSERT INTO MYTABLE(ID, COL2) VALUES(4, 4)
> Error: SQL Exception: Attempt to modify an identity column 'ID'. , SQL St=
ate: 42Z23, Error Code: 30000
> -- Although, this works fine
> INSERT INTO MYTABLE(COL2) VALUES(4)

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