Changing precision of numeric column in Oracle

Question

Currently I have a column that is declared as a NUMBER. I want to change the precision of the column to NUMBER(14,2).

SO, I ran the command

 alter table EVAPP_FEES modify AMOUNT NUMBER(14,2)'

for which, I got an error :

   column to be modified must be empty to decrease precision or scale

I am guessing it wants the column to be empty while it changes the precision and I don't know why it says we want to decrease it while we are increasing it, the data in the columns can't be lost. Is there a short workaround for this? I don't want to copy it into another table and drop it afterwards, or rename a column and copy in between columns, because there is a risk of losing data between the transfers and drops.

Answer 1

Assuming that you didn't set a precision initially, it's assumed to be the maximum (38). You're reducing the precision because you're changing it from 38 to 14.

The easiest way to handle this is to rename the column, copy the data over, then drop the original column:

alter table EVAPP_FEES rename column AMOUNT to AMOUNT_OLD;

alter table EVAPP_FEES add AMOUNT NUMBER(14,2);

update EVAPP_FEES set AMOUNT = AMOUNT_OLD;

alter table EVAPP_FEES drop column AMOUNT_OLD;

If you really want to retain the column ordering, you can move the data twice instead:

alter table EVAPP_FEES add AMOUNT_TEMP NUMBER(14,2);

update EVAPP_FEES set AMOUNT_TEMP = AMOUNT;

update EVAPP_FEES set AMOUNT = null;

alter table EVAPP_FEES modify AMOUNT NUMBER(14,2);

update EVAPP_FEES set AMOUNT = AMOUNT_TEMP;

alter table EVAPP_FEES drop column AMOUNT_TEMP;