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RE: How to get rid of a column default value ?

From: Ron Rogers <RROGERS_at_galottery.org>
Date: Mon, 07 Oct 2002 05:24:26 -0800
Message-ID: <F001.004E2105.20021007052426@fatcity.com>


Dan,
Thanks for the detailed explaination.
Ron

>>> Dan.Fink_at_mdx.com 10/04/02 05:08PM >>>
Setting the default to NULL changes to behavior to be the same as if a default value had not been set. However, in dba_tab_columns, the default_data column would indicate null. If the default value was never set,
the column would be empty (null in type, not name).

The example below demonstrates the behavior:

create table test
(col1 char(4),
 col2 char(4) default 'AAAA');

insert into test values (NULL, NULL);
insert into test values ('1', NULL);
insert into test values ('2', 'BBBB');

select * from test;

COL1 COL2
---- ----

1
2 BBBB insert into test (col1) values ('3');
select col1, length(col1), col2, length(col2) from test;

COL1 LENGTH(COL1) COL2 LENGTH(COL2)
---- ------------ ---- ------------

1               4
2               4 BBBB            4
3               4 AAAA            4

alter table test
modify col2 default NULL;
insert into test (col1) values ('4');

select col1, length(col1), col2, length(col2) from test;

COL1 LENGTH(COL1) COL2 LENGTH(COL2)
---- ------------ ---- ------------

1               4
2               4 BBBB            4
3               4 AAAA            4
4               4

alter table test modify col2 default null

select table_name, column_name, data_default from user_tab_columns
where table_name = 'TEST';

TABLE_NAME COLUMN_NAME DATA_DEFAULT
---------- ----------- ------------

TEST       COL1
TEST       COL2        null

SQL> SQL> alter table test
  2 modify col2 default 'NULL';
SQL> insert into test (col1) values ('5'); SQL> select col1, length(col1), col2, length(col2)   2 from test;

COL1 LENGTH(COL1) COL2 LENGTH(COL2)
---- ------------ ---- ------------

1               4
2               4 BBBB            4
3               4 AAAA            4
4               4
5               4 NULL            4

select table_name, column_name, data_default from user_tab_columns
where table_name = 'TEST';

TABLE_NAME COLUMN_NAME DATA_DEFAULT
---------- ----------- ------------

TEST       COL1
TEST       COL2        'NULL'


-----Original Message-----
Sent: Friday, October 04, 2002 2:38 PM
To: Multiple recipients of list ORACLE-L

Louis,
 I still have not convinced myself that we have the proper answer. If you query the DBA_TAB_COLUMNS table DATA_DEFAULT column you will see
that the original NON default created column has a null or blank as the
value for the data_default column. If the default is set to NULL then the word NULL appears as the data_default value for the column. What if
the column was a char(4) column then it would default to the value"NULL"
which is not the same as blank or nothing. Still digging for an answer.
Ron
ROR mm

>>> Louis_Brouillette_at_UQTR.CA 10/04/02 03:21PM >>>
Thanks Dale, Michael and Ron.

The "default null" is what I thought about first and it almost does the

job. It's just that it appears like there is a default value which is

null. If I don't include the DEFAULT clause, it does nothing. I think

I'll have to live with the "default null".

At 08:29 2002-10-04 -0800, you wrote:
>Louis,
> I believe it is the ALTER TABLE command.
>ALTER TABLE name
>MODIFY ( column datatype);
>match the column name and the datatype but do not include the DEFAULT
>clause .
>Ron
>ROR mm
>
> >>> Louis_Brouillette_at_UQTR.CA 10/04/02 11:28AM >>>
>Anyone knows how to get rid of a column default value ? I rtfm and
>search
>metalink with no luck.

Louis Brouillette
Analyste en informatique (DBA)
Universite du Quebec a Trois-Rivieres
Tel: (819) 376-5011 ext. 2435
Email: brouille_at_uqtr.ca

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Received on Mon Oct 07 2002 - 08:24:26 CDT

Original text of this message

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