SQL> create table brisime (a number constraint pk_br primary key);

Table created.

SQL> insert into brisime values (1);

1 row created.

SQL> -- you can not enter another value = 1
SQL> insert into brisime values (1);
insert into brisime values (1)
*
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.PK_BR) violated


SQL> alter table brisime disable constraint pk_br;

Table altered.

SQL> -- after we disabled the constraint, you can add as many 1s as you want
SQL> insert into brisime values (1);

1 row created.

SQL> insert into brisime values (1);

1 row created.

SQL> commit;

Commit complete.

SQL>