David, Tom,
The problem really is that the two states of not initialized and post first usage are indistinguishable (both return 1), but the sequence next value is different. ie it’s a reasonable expectation that the next value is last_value + 1. IMHO violating this makes it a bug. Further, this situation means there’s no query that can be run on the sequence that can determine if the next value is 1 or 2.
As for existing code relying of current behaviour, given that current behaviour can’t be relied upon to predict the next value, I don’t think it’s possible for any usage to rely on 1 being returned when uninitialized.
I agree though that returning null is a better choice for uninitialized sequences than returning 0.
This whole line of enquiry came about because currval('mytable_id_seq') explodes when called on an uninitialized sequence (another surprise - I was expecting null); how about fixing that too? If that was fixed is would provide a work around for the lack of distinction between the two states of next value being 1 and next value being 2.
Regards,
Glen
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Mon, Mar 7, 2022 at 12:15 AM PG Bug reporting form <
> noreply@postgresql.org> wrote:
>> For a freshly defined sequence, the following:
>> select last_value from mytable_id_seq
>> should return 0, but returns 1.
> One seems as good a choice as zero if a non-null value is to be returned.
The larger point here is that any change is much more likely to
break applications expecting the historical behavior than it is
to make anyone's life better. In a green field I'd tend to
agree that returning NULL (and dispensing with is_called) would
be a better design, but that opportunity was missed decades ago.
regards, tom lane
