Alter varchar2 column to clob

Question

Hi all,
have a table like :
create table test(col1 varchar2(20),col2 number); -- with data
now i have to change col1 to clob.
alter table test modify col1 clob; ... is not working..
can i change the data type to clob without dropping the table .. as it contains huge data.. i will take a lot of time repopulating it..

Answer 1

Hi,
You can cant modify from VARCHAR2 to CLOB but you can achieve your result like this:
1. Add a new column as CLOB
2. UPDATE varchar date to CLOB column;
3. DROP VARCHAR column
4. Rename CLOB column to VARCHAR column name
SQL>CREATE TABLE t ( name VARCHAR2(20), age number(3));
Table created.
SQL>INSERT INTO t VALUES('aaa',20);
1 row created.
SQL>INSERT INTO t VALUES('bbb',30);
1 row created.
SQL>COMMIT;
Commit complete.
SQL>ALTER TABLE t MODIFY name CLOB;
ALTER TABLE t MODIFY name CLOB
ERROR at line 1:
ORA-22858: invalid alteration of datatype
SQL>ALTER TABLE t ADD tmp_name CLOB;
Table altered.
SQL>UPDATE t SET tmp_name=name;
2 rows updated.
SQL>
SQL>ALTER TABLE t DROP COLUMN name;
Table altered.
SQL>
SQL>ALTER TABLE t RENAME COLUMN tmp_name to name;
Table altered.
SQL>
SQL>desc T;
Name                                                  Null?    Type
AGE                                                            NUMBER(3)
NAME                                                           CLOB
SQL>SELECT * FROM  v$version;
BANNER
Oracle9i Enterprise Edition Release 9.2.0.6.0 - 64bit Production
PL/SQL Release 9.2.0.6.0 - Production
CORE    9.2.0.6.0       Production
TNS for Solaris: Version 9.2.0.6.0 - Production
NLSRTL Version 9.2.0.6.0 - Production
5 rows selected.
SQL>Regards