Invisible columns let you add new columns without exposing them to existing applications, letting you insulate new changes from breaking existing code

1. 1
12c

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

3. Feature
invisible columns

4. have been there "forever"

5. function based indexes

6. set column unused

7. SQL> create table T
2 ( x int,
3 y int);
Table created.
SQL> create index IX on T (x+0);
Index created.
SQL> alter table T set unused column Y;
Table altered.

8. SQL> select column_name, data_default
2 from USER_TAB_COLS
3 where table_name = 'T'
4 order by column_id;
COLUMN_NAME DATA_DEFAULT
------------------------------ ----------------
X
SYS_NC00003$ "X"+0
SYS_C00002_14020720:50:28$

9. now exposed to us

10. SQL> create table T ( c1 int, c2 int, c3 int );
SQL> desc T
Name Null? Type
---------------------------- -------- -------
C1 NUMBER(38)
C2 NUMBER(38)
C3 NUMBER(38)
SQL> alter table T modify c1 invisible;
SQL> desc T
Name Null? Type
---------------------------- -------- -------
C2 NUMBER(38)
C3 NUMBER(38)

11. so what's the appeal ?

12. rollout new code online

13. SQL> create table T ( c1 int, c2 int ) ;
Table created.
SQL> create or replace
2 procedure BAD_APP is
3 begin
4 insert into T
5 select object_id, data_object_id
6 from all_objects
7 where rownum < 10;
8 end;
9 /
Procedure created.
SQL> exec BAD_APP;
PL/SQL procedure successfully completed.

14. new application

15. SQL> alter table T add c3 int;
Table altered.
SQL> create or replace
2 procedure NEW_APP is
3 begin
4 for i in ( select c1,c2,c3 from T )
5 loop
6 dbms_output.put_line(i.c1);
7 dbms_output.put_line(i.c2);
8 dbms_output.put_line(i.c3);
9 end loop;
10 end;
11 /
Procedure created.

16. SQL> exec NEW_APP;
28
28
15
15
29
29
25
25
54
PL/SQL procedure successfully completed.

19. SQL> exec BAD_APP
BEGIN BAD_APP; END;
*
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00905: object SCOTT.BAD_APP is invalid
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored

20. SQL> alter table T modify c3 invisible;
Table altered.
SQL> exec NEW_APP;
28
28
15
15
29
29
25
25
54
PL/SQL procedure successfully completed.
SQL> exec BAD_APP;
PL/SQL procedure successfully completed.

21. and an idiosyncracy...

22. SQL> alter table T modify c1 visible;
SQL> desc T
Name Null? Type
---------------------------- -------- -------
C2 NUMBER(38)
C3 NUMBER(38)
C1 NUMBER(38)

23. requires code discipline

24. SQL> desc T
Name Null? Type
---------------------- -------- --------------------
C1 NUMBER(38)
C2 NUMBER(38)
C3 NUMBER(38)
SQL> create or replace
2 procedure P is
3 begin
4 insert into T values (1,10,100);
6 end;
SQL> exec P
SQL> select * from T;
C1 C2 C3
---------- ---------- ----------
1 10 100

25. SQL> alter table T modify c1 invisible;
Table altered.
SQL> alter table T modify c1 visible;
Table altered.
SQL> desc T
Name Null? Type
------------------- -------- --------------------
C2 NUMBER(38)
C3 NUMBER(38)
C1 NUMBER(38)

26. SQL> exec P
PL/SQL procedure successfully completed.
SQL> select c1,c2,c3 from t;
C1 C2 C3
---------- ---------- ----------
1 10 100
100 1 10

27. SQL> create or replace
2 procedure FIX_COLS(p_tab varchar2, p_col_list varchar2) is
3 l_col_list varchar2(1000) := p_col_list||',';
4 type clist is table of varchar2(30)
5 index by pls_integer;
6 c clist;
7
8 l_col varchar2(30);
9 l_id int;
10 begin
11 while instr(l_col_list,',') > 1 loop
12 c(c.count+1) := substr(l_col_list,1,instr(l_col_list,',')-1);
13 l_col_list := substr(l_col_list,instr(l_col_list,',')+1);
14 dbms_output.put_line(c(c.count));
15 end loop;
16
17 for i in 1 .. c.count loop
18 loop
19 select column_name
20 into l_col
21 from user_tab_columns
22 where table_name = p_tab
23 and column_id = i;
24
25 exit when l_col = c(i);
26
27 execute immediate 'alter table '||p_tab||' modify '||l_col||' invisible';
28 execute immediate 'alter table '||p_tab||' modify '||l_col||' visible';
29 end loop;
30 end loop;
31 end;
32 /

28. SQL> exec FIX_COLS('T','C1,C2,C3');
PL/SQL procedure successfully completed.
SQL> desc T
Name Null? Type
---------------------------- -------- -------
C1 NUMBER(38)
C2 NUMBER(38)
C3 NUMBER(38)

29. tools

30. SQL> create table T ( c1 int, c2 int invisible);
Table created.
SQL> desc T
Name Null? Type
------------------------- -------- ------------------
C1 NUMBER(38)
SQL> set colinvisible ON
SQL> desc T
Name Null? Type
------------------------- -------- -----------
C1 NUMBER(38)
C2 (INVISIBLE) NUMBER(38)

32. SQL> alter table T add "C3 (INVISIBLE)" int;
Table altered.
SQL> desc T
Name Null? Type
------------------------- -------- ------------
C1 NUMBER(38)
C3 (INVISIBLE) NUMBER(38)
C2 (INVISIBLE) NUMBER(38)