Modify Primary Key
Sometimes, developers may design a better primary key to support the uniqueness of a table and they want to replace the current one with the new one, but the problem is that there's no syntax to support changing the composition of a primary key directly, so we should take it as two steps, which are:
The only syntax supported by Oracle database is to modify the state of the primary key. For example, to disable the primary key constraint, we can do this:
SQL> alter table hr.job_history modify primary key disable;
Table altered.
Additionally, to disable the primary key constraint as well as the foreign key, we can add CASCADE to it:
SQL> alter table hr.job_history modify primary key disable cascade;
Table altered.