Comments on: I wish

By: David Penington

David Penington — Mon, 03 Jun 2013 23:01:17 +0000

The virtual column is a very nice trick.
My case is the history one, with a current version whose values I want to copy.
Thank you for pointing me to this discussion,

By: Jonathan Lewis

Jonathan Lewis — Thu, 26 Jan 2012 20:47:33 +0000

James,

Nice trick.
Only 11g, of course.

By: Jonathan Lewis

Jonathan Lewis — Thu, 26 Jan 2012 20:47:02 +0000

Matthias,
That’s an interesting one.
Easily visible to the human eye that T is key-preserved (it can only produce one row in the join), but not implemented.
It makes me wonder if there are any other variants of a similar nature – i.e. key-preservation logically created by a predicate even though it isn’t implied by the underlying constraints.

By: Jonathan Lewis

Jonathan Lewis — Thu, 26 Jan 2012 20:41:58 +0000

Sokrates,
Thanks for the example.
One thought, though – the main reason for liking the updateable join view is that it ought to make the “double” subquery unnecessary, i.e. code like:

update t1
set column X = (subquery)
where exists (very similar subquery)

By: James Su

James Su — Wed, 11 Jan 2012 19:21:14 +0000

virtual column:

alter table t1 add (id3 as (1));

update 
    ( 
    select 
        t1.val  v1, 
        t2.val  v2 
    from 
        t1,t2 
    where 
        t1.id1 = t2.id1 
    and t1.id2 = t2.id2 
    and t2.id3 = t1.id3 
)   iv 
set 
    iv.v1 = iv.v2 
;

By: Sokrates

Sokrates — Mon, 09 Jan 2012 13:33:33 +0000

Jonathan,

here is another very simple case where ORA-01779 is raised unjustifiedly:

create table t(
   id int,
   attr varchar2(10),
   constraint t_pk primary key(id)
);   

create table l(
   id int,
   k int,
   s varchar2(10),
   constraint l_pk primary key(id, k),
   constraint l_fk foreign key(id) references t(id)
);   

insert into t(id, attr) values(1, 'aaa');

update
(
   select t.id, t.attr
   from t, l
   where l.id(+)=t.id
   and l.k(+)=1
   and l.id is null
)
set attr = 'bbb';

gives (11.2.0.2) ORA-01779: cannot modify a column which maps to a non key-preserved table

a workaround would be

update
(
   select t.id, t.attr
   from t
   where not exists(select null from l where l.id = t.id and l.k=1)
)
set attr = 'bbb'

Matthias

By: Sokrates

Sokrates — Fri, 06 Jan 2012 20:34:24 +0000

[sourcecode] sokrates@11.2.0.2 > update 2 ( 3 select 4 t1.val v1, 5 t2.val v2 6 from 7 t1,t2 8 where 9 t1.id1 = t2.id1 10 and t1.id2 = t2.id2 11 and t2.id3 = 1 12 ) iv 13 set 14 iv.v1 = iv.v2 15 ; iv.v1 = iv.v2 * ERROR at line 14: ORA-01779: cannot modify a column which maps to a non key-preserved table sokrates@11.2.0.2 > REM so, we do the equivalent sokrates@11.2.0.2 > update 2 ( 3 select 4 t1.val v1, 5 (select t2.val from t2 6 where 7 t1.id1 = t2.id1 8 and t1.id2 = t2.id2 9 and t2.id3 = 1 10 ) v2 11 from 12 t1 13 where (t1.id1, t1.id2) in 14 ( 15 select t2.id1, t2.id2 16 from t2 17 where t2.id3 = 1 18 ) 19 ) iv 20 set 21 iv.v1 = iv.v2 22 ; 1 row updated. [/sourcecode]