Re: safely exchanging primary keys?

Louis-David Mitterrand <vindex+lists-pgsql-sql(at)apartia(dot)org> wrote:

> I have this function which swaps primary keys for cabin_types (so that
> id_cabin_type ordering reflects natural data ordering):

> CREATE OR REPLACE FUNCTION swap_cabin_types(id1 integer, id2 integer) RETURNS integer
> AS $$
> declare
> tmp integer;
> begin
> tmp := nextval('cabin_type_id_cabin_type_seq');
> update cabin_type set id_cabin_type=tmp where id_cabin_type=id1;
> update cabin_type set id_cabin_type=id1 where id_cabin_type=id2;
> update cabin_type set id_cabin_type=id2 where id_cabin_type=tmp;
> return tmp;
> end;
> $$
> LANGUAGE plpgsql;

> 'id_cabin_type' is a foreign key for two other tables, 'cabin_category'
> and 'alert_cabin_type', which have an "on update cascade" clause.

> When I run that function it seems the foreign keys are not properly
> updated and the data ends up in a mess.

> Did I forget something?

What does "are not properly updated" mean? Anyhow, why don't
you use something simple like (untested):

| UPDATE cabin_type
| SET id_cabin_type =
| CASE
| WHEN id_cabin_type = id1 THEN
| id2
| ELSE
| id1
| END
| WHERE id_cabin_type IN (id1, id2);

Tim