In oracle 12c TRUNCATE TABLE CASCADE will truncate its child tables, if ON DELETE CASCADE relationship is present on child table.

Create one parent and child table with some data

SQL> CREATE TABLE DBATEST ( EMPNO number, NAME varchar2(10) , empid number);

Table created.
	
SQL> alter table dbatest add constraint emp_pk primary key ( empid);

Table altered.

													   NOT NULL 
SQL> CREATE TABLE DBACHILD ( EMPID number, dept number);

Table created.


--- add the delete cascade keyword while adding foreign key constraint

SQL> alter table dbachild add constraint child_fk foreign key ( EMPID ) REFERENCES dbatest(EMPID) on delete cascade;

Table altered.


SQL> insert into dbatest values ( 1,'RAJ',1);

1 row created.

SQL> insert into dbatest values ( 1,'RAM',2);

1 row created.

SQL> insert into dbatest values ( 1,'RAM',3);

1 row created.

SQL> commit;

Commit complete.


SQL> insert into dbachild values ( 1,2);

1 row created.

SQL> insert into dbachild values ( 2,2);

1 row created.

SQL> commit;     

Commit complete.

SQL> select count(*) from dbatest;

  COUNT(*)
----------
	 3

SQL> select count(*) from dbachild;

  COUNT(*)
----------
	 2

You can check the child table details using : Get child table details

OWNER CHILD_TABL STATUS FK_COLUMN CONSTRAINT_NAME
---------- ---------- -------- --------------- ---------------------------
TEST DBACHILD ENABLED EMPID CHILD_FK

– Truncate the parent table with cascade option:

SQL> truncate table dbatest cascade;

Table truncated.

SQL> select count(*) from dbatest;

  COUNT(*)
----------
	 0


SQL> select count(*) from dbachild;

  COUNT(*)
----------
	 0

We can see the child table has been truncated, though we just truncated only parent table.