SQL> drop table b1;

Table dropped.

SQL> create table b1 (x int, y int);

Table created.

SQL> insert into b1  select 1, 1 from dual
  2                  union
  3                  select 1, 2 from dual
  4                  union
  5                  select 2, 1 from dual;

3 rows created.

SQL>
SQL> alter table b1 add constraint b1pk primary key (x) deferrable;
alter table b1 add constraint b1pk primary key (x) deferrable
                              *
ERROR at line 1:
ORA-02437: cannot validate (HR.B1PK) - primary key violated

SQL> alter table b1 add constraint b1pk primary key (x) enable novalidate;
alter table b1 add constraint b1pk primary key (x) enable novalidate
                              *
ERROR at line 1:
ORA-02437: cannot validate (HR.B1PK) - primary key violated

SQL> create index b1pk on b1(x);

Index created.

SQL>
SQL> alter table b1 add constraint b1pk primary key (x) enable novalidate;

Table altered.

FOO SCOTT>select * from EMPLOYEE;

DEPRATMENT_ID     EMP_ID
------------- ----------
            1         10
            1         20
            1         30
            1         40
            2         50
            2         60
            2         70
            2         80
            3         90
            3         11
            4         13
            5         14
            5         15
            5         16
            5         17
            5         18

16 rows selected.

FOO SCOTT>alter table EMPLOYEE add constraint foo11 primary key (DEPRATMENT_ID) deferrable novalidate;

Table altered.