[DERBY-6545] Should not be able to add a default to an identity column

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 10.11.1.1
• Component/s: SQL
• Labels: derby_backport_reject_10_10
• Urgency: Normal
• Issue & fix info: Release Note Needed, Repro attached
• Bug behavior facts: Deviation from standard
• Assignee: Richard N. Hillegas
• Reporter: Richard N. Hillegas
• Created: 17/Apr/14 19:16
• Updated: 09/Sep/16 09:53
• Resolved: 30/May/14 14:32

Description

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:

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

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.

Issue Links

• is duplicated by: DERBY-4011 ALTER COLUMN is only allowed to change default value of some types of generated columns