Converting a number column to a varchar2

Question

Hi ,
We are on 11.2.0.2 on Solaris 10. I have a need to convert a column which is a number data type to a VARCHAR2 data type. The table has data and the column is part of the primary key. Is it possible? How best can one go about it?
SQL>  create table test1
(object_name varchar2(30) NOT NULL, object_id number NOT NULL);
Table created.
SQL>ALTER TABLE TEST1 add(constraint test1_pk primary key (OBJECT_NAME,OBJECT_ID));
Table altered.
SQL> INSERT INTO TEST1 VALUES('EMP',1);
1 row created.
SQL> ED
Wrote file afiedt.buf
  1* INSERT INTO TEST1 VALUES('DEPT',2)
SQL> /
1 row created.
SQL> COMMIT;
Commit complete.
SQL> ALTER TABLE TEST1 MODIFY (OBJECT_ID VARCHAR2(20));
ALTER TABLE TEST1 MODIFY (OBJECT_ID VARCHAR2(20))
ERROR at line 1:
ORA-01439: column to be modified must be empty to change datatype

Answer 1

You can use following steps:
1. create a new temporary column of right data type in existing table
2. copy existing data to new temp. column
3. drop table primary key
4. nullify all data in current column
5. change current column data type
6. copy data from temp. column to current column
7. drop temporary column
8. add primary key
Example:
SQL> create table t(x number primary key);
Table created.
SQL> insert into t values(1);
1 row created.
SQL> insert into t values(2);
1 row created.
SQL> commit;
Commit complete.
SQL> --
SQL> alter table t add (tmp varchar2(10));
Table altered.
SQL> update t set tmp = x;
2 rows updated.
SQL> commit;
Commit complete.
SQL> alter table t drop primary key;
Table altered.
SQL> update t set x = null ;
2 rows updated.
SQL> commit;
Commit complete.
SQL> alter table t modify (x varchar2(10));
Table altered.
SQL> update t set x=tmp;
2 rows updated.
SQL> alter table t drop column tmp;
Table altered.
SQL> alter table t add primary key(x);
Table altered.
SQL> --
SQL> desc t
Name                                      Null?    Type
X                                         NOT NULL VARCHAR2(10)
SQL> select * from t;
X
1
2Edited by: P. Forstmann on 30 oct. 2012 09:38