Truncating a simple table is easy....But truncating a table that has a declarative referential integrity constraint has always been difficult. 12c introduces the CASCADE option to assist

2. 2

3. 3

4. 4
better truncate in 12c

5. 5
SQL> create table PARENT ( p int primary key );
Table created.
SQL> create table CHILD
2 ( c int primary key,
3 p int references PARENT ( p )
4 );
Table created.

6. 6
SQL> insert into PARENT values (1);
1 row created.
SQL> insert into CHILD values (1,1);
1 row created.

7. 7
SQL> truncate table PARENT;
truncate table PARENT
*
ERROR at line 1:
ORA-02266: unique/primary keys in table
referenced by enabled foreign keys

8. 8
SQL> create table CHILD
2 ( c int primary key,
3 p int references PARENT ( p )
4 on delete cascade);
Table created.

9. 9
SQL> insert into PARENT values (1);
1 row created.
SQL> insert into CHILD values (1,1);
1 row created.
SQL> truncate table PARENT;
truncate table PARENT
*
ERROR at line 1:
ORA-02266: unique/primary keys in table referenced by
enabled foreign keys

10. 10
disable the constraint

11. 11
SQL> alter table CHILD
2 disable constraint CHILD_FK;
Table altered.
SQL> truncate table PARENT;
Table truncated.

12. 12
but ...

13. 13
SQL> alter table CHILD
2 enable constraint CHILD_FK;
ERROR at line 1:
ORA-02298: cannot validate (CHILD_FK)
parent keys not found

14. 14
can 12c help ?

15. 15
SQL> truncate table PARENT
Table truncated.
SQL> select count(*) cnt
2 from CHILD;
CNT
---------
0
cascade;

16. 16
must be on delete cascade

17. 17
might need to recreate

18. 18
SQL> alter table child modify
2 constraint CHILD_FK on delete cascade;
ERROR at line 1:
ORA-00933: SQL command not properly ended

19. 19
SQL> alter table child add
2 constraint NEW_FK foreign key ( p )
3 references parent ( p ) on delete cascade;
ERROR at line 1:
ORA-02275: such a referential constraint already
exists in the table

20. 20
full cascade

21. 21
...

22. 22
be careful !

23. 23
referential partitions

24. 24