SQL> create table parent as select level n from dual connect by level <= 5
  2  /

Table created.

SQL> alter table parent add constraint parent_pk primary key(n)
  2  /

Table altered.

SQL> create table child as select level n from dual connect by level <= 5
  2  /

Table created.

SQL> alter table child add constraint child_fk1 foreign key(n) references parent
  2  /

Table altered.

SQL> delete parent where n > 3
  2  /
delete parent where n > 3
*
ERROR at line 1:
ORA-02292: integrity constraint (SCOTT.CHILD_FK1) violated - child record found


SQL> alter table child disable constraint child_fk1
  2  /

Table altered.

SQL> delete parent where n > 3
  2  /

2 rows deleted.

SQL> alter table child enable novalidate constraint child_fk1
  2  /

Table altered.

SQL> select * from parent
  2  /

         N
----------
         1
         2
         3

SQL> select * from child
  2  /

         N
----------
         1
         2
         3
         4
         5

SQL> insert into child values(5)
  2  /
insert into child values(5)
*
ERROR at line 1:
ORA-02291: integrity constraint (SCOTT.CHILD_FK1) violated - parent key not found


SQL>