PostgreSQL: Update primary key, avoid conflict

Question

I want to update the primary key in several rows of a table. If all rows were updated, the key would be unique again, but the update of the first row results in a temporary conflict with the key of the second row. Is there an elegant way to solve this?

Example:

create table erichtest ( i integer, v varchar(200) );
alter table erichtest add constraint pk_erichtest primary key(i);
insert into erichtest values(1, 'Eins');
insert into erichtest values(2, 'Zwei');
update erichtest set i=i+1;

ERROR: duplicate key value violates unique constraint "pk_erichtest"

Answer 1

Something like this should help:

b=# begin;
BEGIN
b=# alter table erichtest drop constraint pk_erichtest ;
ALTER TABLE
b=#  alter table erichtest add constraint pk_erichtest primary key (i) DEFERRABLE INITIALLY IMMEDIATE;
ALTER TABLE
b=# set constraints pk_erichtest deferred ;
SET CONSTRAINTS
b=# update erichtest set i=i+1;
UPDATE 2
b=# select * from erichtest ;
 i |  v
---+------
 2 | Eins
 3 | Zwei
(2 rows)

b=# end;
COMMIT