How to set two primary keys in one table in oracle?

Question

set one primary key at table creation and another one is after creation of primary key.

Answer 1

You can add a unique constraint...even several...

Answer 2

create table tablename (column1, column2 , primary key(column1,column2))

Answer 3

One table can only have only one Primary Key, but can have more than 1 foreign key.
2 primary key is not necessary practically too.