Evaluate the following ALTER TABLE statement:
ALTER TABLE orders
SET UNUSED order_date;
Which statement is true?
A.
The DESCRIBE command would still display the ORDER_DATE column.
B.
ROLLBACK can be used to get back the ORDER_DATE column in the ORDERS table.
C.
The ORDER_DATE column should be empty for the ALTER TABLE command to execute successfully.
D.
After executing the ALTER TABLE command, you can add a new column called ORDER_DATE to the ORDERS table.
C .. the unused column is not empty, but it is disappeared and not exist in table anymore, so it is not empty.
create table ou1 (o number, a number, b number);
desc ou1;
ALTER TABLE ou1 SET UNUSED (a);
ALTER TABLE ou1 add (a number);
D