> > I know deferred constraints would solve it, but is there any other way in the absence of it? Assigning an out-of-domain value is not acceptable, since it breaks the domain definition. Thanks.
>
> Maybe you could swap (update) values of all other columns and leave the
> unique column as it is?

Twisted :) But I can't, since one of the other columns will always have a PK constraint on it.

For example, the ORDER_INDEX column is used for custom ordering of values. I want to be able to move a row's position in the dataset updating that column.