Change column datatype from varchar2 to number(10) and keep existing data

Question

Hi,
I need to change the datatype on a column that already has data in it from a varchar2 to number(10). The data that is already there is not necessarily number data, however I must be able to keep the old data to. We are running 10g. Does anyone have any ideas? Thanks. Here's the current data.
Current Values for From_Value
T
U
T2
K
M
A
T
T1
O
E
S
NSTU
4

Answer 1

Example of keeping the data in the current column and adding a new numeric column for numeric data:
SQL> drop table t purge;
Table dropped.
SQL> create table t(i int, x varchar2(10));
Table created.
SQL> insert into t values(1, 'T1');
1 row created.
SQL> insert into t values(2, 2);
1 row created.
SQL> --
SQL> alter table t add (xn number);
Table altered.
SQL> --
SQL> begin
  2  for c in (select i, x from t)
  3  loop
  4   begin
  5   update t set xn = to_number(c.x) where i = c.i;
  6   exception
  7    when invalid_number then null;
  8   end;
  9  end loop;
10  end;
11  /
PL/SQL procedure successfully completed.
SQL> show errors
No errors.
SQL> select * from t;
         I X                  XN
         1 T1
         2 2                   2