How to change the datatype of a column having lots of data.

Question

My table :: select hrm_employeeentitlement_id, amount FROM hrm_employeeentitlement;
need to change the Amount column :(
From :: amount Number(18,0)
To :: amount Number(10,2)
I am using 10XE
thanks in advance
w\

Answer 1

create a "temp" backup of your table, drop the original and create a new table. Fill this one with the "temp"
SQL> create table t
  2  (amount number (18,0))
  3  /
Table created.
SQL> insert into t
  2  select rownum
  3    from all_objects
  4   where rownum <= 10
  5  /
10 rows created.
SQL> commit
  2  /
Commit complete.
SQL> alter table t
  2  modify (amount number (10,2))
  3  /
modify (amount number (10,2))
ERROR at line 2:
ORA-01440: column to be modified must be empty to decrease precision or scale
SQL> create table temp
  2  as
  3  select *
  4    from t
  5  /
Table created.
SQL> drop table t
  2  /
Table dropped.
SQL> create table t
  2  (amount number (10,2))
  3  /
Table created.
SQL> insert into t
  2  select *
  3    from temp
  4  /
10 rows created.
SQL> drop table temp purge
  2  /
Table dropped.