drop table T;
create table T (id integer not null primary key, name varchar(10));
insert into T(1, 'a');

create table TDetails (id integer not null primary key, tid integer constraint "TDetails.tid" references T (id));
insert into TDetails(1, 1);
insert into T(2, 1);

alter table TDetails drop constraint "TDetails.tid";
alter table TDetails alter column tid to tid1;
alter table TDetails add constraint "TDetails.tid1" foreign key (tid1) references T (id);
alter table TDetails add column V integer;
update TDetails set V = tid1;

drop table T;
create table T (id integer not null primary key, name varchar(10));
insert into T(1, 'a');

create table TDetails (id integer not null primary key, tid integer constraint "TDetails.tid" references T (id));
insert into TDetails(1, 1);
insert into TDetails(2, 1); -- ошибочка

alter table TDetails drop constraint "TDetails.tid";
alter table TDetails alter column tid to tid1;
alter table TDetails add constraint "TDetails.tid1" foreign key (tid1) references T (id);
alter table TDetails add column V integer;
update TDetails set V = tid1;