Whenever you try to change your NUMBER column to more specific scale like NUMBER(10,2) you end up with an error message:
SQL Error: ORA-01440: column to be modified must be empty to decrease precision or scale
There is a way out of this but it is a bit hacky. Let me know if there is a more elegant solution!
Following example also takes care of the situation when your column is not nullable.
alter table MYTABLE add AMOUNT_TEMP NUMBER; update MYTABLE set AMOUNT_TEMP = AMOUNT; alter table MYTABLE modify AMOUNT NULL; update MYTABLE set AMOUNT=null; alter table MYTABLE modify AMOUNT number(10,2); update MYTABLE set AMOUNT=AMOUNT_TEMP; alter table MYTABLE modify AMOUNT NOT NULL; alter table MYTABLE drop column AMOUNT_TEMP;