Thread: Deferral of primary key constraint

Is it possible to defer the check on a primary key constraint (or a check constraint, for that matter).  Here is an example that shows why it would be nice to be able to do so.  We have a real-life scenario that is similar (but much more complex).

drop table btab;
create table btab (
    base        varchar,
    pos         int4,
    cmt         varchar,

   primary key (base, pos)
);

insert into btab (base,pos,cmt) values ('aa',1,'The');
insert into btab (base,pos,cmt) values ('aa',2,'quick');
insert into btab (base,pos,cmt) values ('aa',3,'grey');
insert into btab (base,pos,cmt) values ('aa',4,'fox');

insert into btab (base,pos,cmt) values ('bb',3,'dog');
insert into btab (base,pos,cmt) values ('bb',2,'brown');
insert into btab (base,pos,cmt) values ('bb',1,'The');

select * from btab order by base,pos;

begin;
delete from btab where base = 'aa' and pos = 2;
update btab set pos = pos - 1 where pos > 2 and base = 'aa';
commit;

select * from btab order by base,pos;

begin;
update btab set pos = pos + 1 where pos >= 2 and base = 'bb';
insert into btab (base,pos,cmt) values ('bb',2,'slow');
commit;

select * from btab order by base,pos;

The last transaction fails (on my box, anyway) because of the primary key index.

We would like to be able to do inserts/deletes to a list of records and still ensure that they are in contiguous sequential order so we want to renumber higher records if a new record is inserted in the middle.  The sequence is part of the primary key and we want to ensure uniqueness.  Some renumbering will work (by chance) if the records happen to get adjusted in the right order.  But if one of the updates tries to rename to an already existing record, it fails.

How hard is it to take the deferral mechanism you have for foreign key references and apply it to the primary key too?  It would also be handy to be able to defer a check constraint.
 

Kyle Bateman wrote:
> Is it possible to defer the check on a primary key constraint (or a
> check constraint, for that matter).  Here is an example that shows why
> it would be nice to be able to do so.  We have a real-life scenario that
> is similar (but much more complex).
   Not  yet.  Only  the  trigger  based  foreign  key checks are   deferrable in 7.0.  We discovered the need for
deferrability  of  UNIQUE  (what  is  what  you want from the PK things) and   other checks. Not sure up to now how we
coulddo  it,  but  a   known problem.
 


Jan

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