Re: ALTER TABLE .. DETACH PARTITION CONCURRENTLY

On Sun, Mar 21, 2021 at 03:01:15PM -0300, Alvaro Herrera wrote:
> > But note that it doesn't check if an existing constraint "implies" the new
> > constraint - maybe it should.
>
> Hm, I'm not sure I want to do that, because that means that if I later
> have to attach the partition again with the same partition bounds, then
> I might have to incur a scan to recheck the constraint. I think we want
> to make the new constraint be as tight as possible ...

If it *implies* the partition constraint, then it's at least as tight (and
maybe tighter), yes ?

I think you're concerned with the case that someone has a partition with
"tight" bounds like (a>=200 and a<300) and a check constraint that's "less
tight" like (a>=100 AND a<400). In that case, the loose check constraint
doesn't imply the tighter partition constraint, so your patch would add a
non-redundant constraint.

I'm interested in the case that someone has a check constraint that almost but
not exactly matches the partition constraint, like (a<300 AND a>=200). In that
case, your patch adds a redundant constraint.

I wrote a patch which seems to effect my preferred behavior - please check.

--
Justin