I need to swap a primary key value, for example:

create table test (

 id int not null default 0,

  other varchar(255) not null default '',

 primary key(id)

);

insert into test (1,'a');

insert into test (2,'b');

now i want that (2,'b') becomes (1,'b') and (1,'a') becomes (2,'a')

the point is, how to do this, with only one UPDATE without duplicate column id value? and without delete values?
--