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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-6545) Should not be able to add a default to an identity column
Date Thu, 17 Apr 2014 19:18:14 GMT
Rick Hillegas created DERBY-6545:
------------------------------------

             Summary: Should not be able to add a default to an identity column
                 Key: DERBY-6545
                 URL: https://issues.apache.org/jira/browse/DERBY-6545
             Project: Derby
          Issue Type: Bug
          Components: SQL
            Reporter: Rick Hillegas
             Fix For: 10.11.0.0


According to the 2011 edition of the SQL Standard, the only alterations allowed on identity
columns are the following:

1) changing the identity properties of the column

2) causing the column to cease to be an identity column

This is described in part 2, section 11.2 (alter column definition), syntax rule 6. However,
Derby allows you to add a default to an identity column. It's clear from the CREATE TABLE
syntax that a column can't both have a default and be an identity column. A side-effect of
using ALTER TABLE to add a default to an identity column is this: the column ceases to be
an identity column. The following script output shows this Derby behavior:

{noformat}
ij version 10.11
ij> connect 'jdbc:derby:memory:db;create=true';
ij> create table t1_01
(
    a int generated always as identity ( start with 10, increment by 20 ),
    b int
);
0 rows inserted/updated/deleted
ij> -- should not succeed but does
alter table t1_01 alter column a default 99;
0 rows inserted/updated/deleted
ij> mainline (1.8) > runsql zzz
ij version 10.11
ij> connect 'jdbc:derby:memory:db;create=true';
ij> create table t1_01
(
    a int generated always as identity ( start with 10, increment by 20 )
);
0 rows inserted/updated/deleted
ij> select c.autoincrementvalue, c.autoincrementstart, c.autoincrementinc, c.columndefault
from sys.syscolumns c, sys.systables t
where c.referenceid = t.tableid
and t.tablename = 'T1_01';
AUTOINCREMENTVALUE  |AUTOINCREMENTSTART  |AUTOINCREMENTINC    |COLUMNDEFAULT  
------------------------------------------------------------------------------
10                  |10                  |20                  |NULL           

1 row selected
ij> -- should not succeed but does
alter table t1_01 alter column a default 99;
0 rows inserted/updated/deleted
ij> select c.autoincrementvalue, c.autoincrementstart, c.autoincrementinc, c.columndefault
from sys.syscolumns c, sys.systables t
where c.referenceid = t.tableid
and t.tablename = 'T1_01';
AUTOINCREMENTVALUE  |AUTOINCREMENTSTART  |AUTOINCREMENTINC    |COLUMNDEFAULT  
------------------------------------------------------------------------------
NULL                |NULL                |NULL                |99             

1 row selected
{noformat}

Fixing this deviation from the Standard will create a backward incompatibility. However, it
is hard to imagine that any production application relies on this deviation. This is the sort
of schema evolution which one tests out in the laboratory or resorts to during an application
upgrade. A judicious use of RENAME COLUMN and ALTER TABLE should provide a usable workaround.

For that reason, I think that we should correct this deviation.



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