SQL> create table master
  2  (id number primary key,
  3   name varchar2(20));

Table created.

SQL> create table detail
  2  (id_fk number constraint fk_dm references master (id),
  3   value number);

Table created.

SQL> insert all
  2    into master (id, name) values (1, 'Little')
  3    into master (id, name) values (2, 'Foot')
  4    into detail (id_fk, value) values (1, 10)
  5    into detail (id_fk, value) values (1, 20)
  6    into detail (id_fk, value) values (2, 30)
  7  select * From dual;

5 rows created.

SQL> commit;

Commit complete.

SQL> select * from master;

        ID NAME
---------- --------------------
         1 Little
         2 Foot

SQL> select * from detail;

     ID_FK      VALUE
---------- ----------
         1         10
         1         20
         2         30

SQL>

SQL> delete from master where id = 1;
delete from master where id = 1
*
ERROR at line 1:
ORA-02292: integrity constraint (SCOTT.FK_DM) violated - child record found

SQL> alter table detail drop constraint fk_dm;

Table altered.

SQL> alter table detail add constraint fk_dm foreign key (id_fk)
  2  references master (id) on delete cascade;

Table altered.

SQL> delete from master where id = 1;

1 row deleted.

SQL> select * from master;

        ID NAME
---------- --------------------
         2 Foot

SQL> select * From detail;

     ID_FK      VALUE
---------- ----------
         2         30

SQL>

create table detail2
   (id_fk number ,
     value number,
constraint fk_dm2 foreign key(id) references master(id) on delete cascade);

insert all
into detail2 values(1,100)
into detail2 values(2,50)

delete from master where id=1

select * from master
/
select * from detail
/
select * from detail2