--- In firebird-support@yahoogroups.com, Dimitry Sibiryakov <sd@...> wrote:

>
> > Obviously to preserve the custom ordering. Two rows of same ORDER_INDEX don't have a definite order.
>
> But how they can get the same value if you handle ORDER_INDEX properly?
> I mean that unique constraints are supposed to prevent serious data
> problems. Custom ordering isn't critical enough.
>
> SY, SD.
>

It's serious as any consistency problem on any state domain. In this particular case, two rows with the same ORDER_INDEX value would prevent re-ordering from working on the client app.