This document discusses improvements to default values and identity columns in Oracle 12c. Key points include: - Triggers are no longer needed to generate primary keys before insert since identity columns can be defined to automatically generate and assign values. - Default values can now be applied conditionally using the ON NULL syntax to control whether the default is applied when a null value is inserted. - Performance of inserts improved by removing the overhead of triggers and allowing defaults to handle null value handling.

1. 1
12c

2. 2
the focus ...
the day to day stuff

3. 3
Feature
defaults

4. 4
the most common ...

5. 5
and the absolute worst ...

6. 6
usage of triggers

7. 7
SQL> create sequence seq;
Sequence created.
SQL> create table T ( pk number , c1 int);
Table created.
SQL> create or replace
2 trigger FILL_IN_PK
3 before insert on T
4 for each row
5 begin
6 select seq.nextval into :new.pk from dual;
7 end;
8 /
Trigger created.

8. 8
SQL> insert into T values (10,20);
1 row created.
SQL> select * from T;
PK C1
---------- ----------
1 20

9. 9
we got smarter

10. 10
SQL> create or replace
2 trigger FILL_IN_PK
3 before insert on T
4 for each row
5 when ( new.pk is null )
6 begin
7 select seq.nextval into :new.pk from dual;
8 end;
9 /
SQL> insert into T values (20,20);
SQL> select * from T;
PK C1
---------- ----------
1 20
20 20

11. triggers

12. over rated ...
for that stuff

13. insert /* with trigger */ into T
select rownum, rownum
from dual connect by level <= 50000
call count cpu elapsed disk query current
------- ------ -------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0
Execute 1 5.64 5.64 0 466 1608
Fetch 0 0.00 0.00 0 0 0
------- ------ -------- ---------- ---------- ---------- ----------
total 2 5.64 5.65 0 466 1608

14. insert /* without trigger */ into T
select rownum, rownum
from dual connect by level <= 50000
call count cpu elapsed disk query current
------- ------ -------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0
Execute 1 0.09 0.15 0 466 1620
Fetch 0 0.00 0.00 0 0 0
------- ------ -------- ---------- ---------- ---------- ----------
total 2 0.09 0.15 0 466 1620

15. 12c

16. 16
SQL> create table T (
2 pk number default seq.nextval,
3 c1 int);
Table created.

17. 17
SQL> insert into T ( c1 ) values ( 0);
SQL> select * from T;
PK C1
---------- ----------
2 0
SQL> insert into T ( pk, c1 ) values (default, 1) ;
SQL> select * from T;
PK C1
---------- ----------
2 0
3 1

18. insert /* with default */ into T
select rownum, rownum
from dual connect by level <= 50000
call count cpu elapsed disk query current
------- ------ -------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0
Execute 1 0.06 0.07 0 467 1608
Fetch 0 0.00 0.00 0 0 0
------- ------ -------- ---------- ---------- ---------- ----------
total 2 0.06 0.08 0 467 1608

19. currval as well

20. 20
SQL> create table PAR (
2 par_id int default par_seq.nextval primary key,
3 par_name varchar2(10)
4 );
Table created.
SQL> create table CHD (
2 chd_id int default chd_seq.nextval primary key,
3 par_id int default par_seq.currval
4 references PAR(par_id),
5 chd_name varchar2(10)
6 );
Table created.

21. 21
SQL> insert into PAR (par_name) values ( 'SPDG' );
SQL> insert into CHD (chd_name) values ( 'Mike K' );
SQL> insert into CHD (chd_name) values ( 'Don' );
SQL> insert into CHD (chd_name) values ( 'Mel' );
SQL> insert into PAR (par_name) values ( 'CORE' );
SQL> insert into CHD (chd_name) values ( 'Gerald' );
SQL> insert into CHD (chd_name) values ( 'Mike H' );

22. 22
SQL> select * from CHD;
CHD_ID PAR_ID CHD_NAME
---------- ---------- ----------
1 1 Mike K
2 1 Don
3 1 Mel
4 2 Gerald
5 2 Mike H

23. other default improvements

24. "identity"

25. 25
SQL> drop table t purge;
Table dropped.
SQL> create table T
2 ( pk number generated as identity ,
3 c1 int);
Table created.
SQL> select object_id, object_name,
2 object_type from user_objects;
OBJECT_ID OBJECT_NAME OBJECT_TYPE
---------- ------------------ ------------
414914 T TABLE
414915 ISEQ$$_414914 SEQUENCE

26. 26
SQL> @pr "select * from user_sequences"
SEQUENCE_NAME : ISEQ$$_414914
MIN_VALUE : 1
MAX_VALUE : 9999999999999999999999
INCREMENT_BY : 1
CYCLE_FLAG : N
ORDER_FLAG : N
CACHE_SIZE : 20
LAST_NUMBER : 1
PARTITION_COUNT :
SESSION_FLAG : N
KEEP_VALUE : N

27. 27
SQL> create table T
2 ( pk number
3 generated as identity (cache 1000)
4 , c1 int);
Table created.
SQL> insert into T values (1,2);
insert into T values (1,2)
*
ERROR at line 1:
ORA-32795: cannot insert into a generated always
identity column

28. more null control

29. before 12c

30. 30
SQL> create table T (
2 pk int,
3 status varchar2(1) default 'N' );
Table created.
SQL> insert into T (pk) values (1);
1 row created.
SQL> insert into T (pk, status) values (2,default);
1 row created.
SQL> insert into T (pk, status) values (3,null);
1 row created.

31. 31
SQL> select * from T;
PK STATUS
---------- ------
1 N
2 N
3

32. workarounds ugly

33. 33
SQL> create or replace
2 procedure ins(p_pk int, p_status varchar2) is
3 begin
4 if p_status is null then
5 insert into T (pk, status)
6 values (p_pk, default );
7 else
8 insert into T (pk, status)
9 values (p_pk, p_status );
10 end if;
11 end;
12 /
Procedure created.

34. 12c "on null"

35. 35
SQL> create table T (
2 pk int,
3 status varchar2(1) default on null 'N' ,
4 start_date date default on null
5 trunc(sysdate,'MM'),
6 commission int default on null 1000,
7 job_level int default on null 1
8 );
Table created.
SQL> insert into T values (1,null,null,null,null);
1 row created.
SQL> select * from T;
PK S START_DAT COMMISSION JOB_LEVEL
---------- - --------- ---------- ----------
1 N 01-JAN-14 1000 1