11g Enhancement for ALTER TABLE .. ADD COLUMN Functionality

Before Oracle 11g adding new columns with DEFAULT values and NOT NULL constraint required both an exclusive lock on the table and the default value to be stored in all existing records.

Now in Oracle 11g the database can optimize the resource usage and storage requirements for this operation, the default value is stored in the data dictionary instead of updating the table column as a result especially for large tables the execution time is reduced and space is saved.

In addition, the following ADD COLUMN operations can now run concurrently with DML operations:
* Add a NOT NULL column with a default value
* Add a nullable column without a default value
* Add a virtual column

release 1002000300 –

drop table tst_source purge ;
create table tst_source nologging as
select rownum id, text
  from dba_source;

set timing on

ALTER TABLE tst_source ADD (name VARCHAR2(16) DEFAULT 'N' NOT NULL);

Elapsed: 00:00:30.43

set timing off

exec dbms_stats.gather_table_stats(user, 'tst_source');

select count(*) from tst_source where name is NULL ;

  COUNT(*)
----------
         0

release 1101000600 –

drop table tst_source purge ;
create table tst_source nologging as
select rownum id, text
  from dba_source;

set timing on

ALTER TABLE tst_source ADD (name VARCHAR2(16) DEFAULT 'N' NOT NULL);

Elapsed: 00:00:00.10

set timing off

exec dbms_stats.gather_table_stats(user, 'tst_source');

select count(*) from tst_source where name is NULL ;

  COUNT(*)
----------
         0