On Sat, Apr 10, 2021 at 01:42:26PM -0500, Justin Pryzby wrote: > 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.
On Sat, Apr 10, 2021 at 02:13:26PM -0500, Justin Pryzby wrote: > I suppose the docs should be updated for the exact behavior, maybe even > without > this patch: > > |A <literal>CHECK</literal> constraint > |that duplicates the partition constraint is added to the partition. I added this as an Opened Item, since it affects user-visible behavior: whether or not a redundant, non-equal constraint is added. -- Justin
