Re: [PATCH] Keeps tracking the uniqueness with UniqueKey

On Fri, Apr 3, 2020 at 12:08 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:

> On Fri, 3 Apr 2020 at 16:40, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > (It occurs to me BTW that we've been overly conservative about using
> > NOT NULL constraints in planning, because of failing to consider that.
> > Addition or drop of NOT NULL has to cause a change in
> > pg_attribute.attnotnull, which will definitely cause a relcache inval
> > on its table, cf rules in CacheInvalidateHeapTuple(). So we *don't*
> > need to have a pg_constraint entry corresponding to the NOT NULL, as
> > we've mistakenly supposed in some past discussions.)
>
> Agreed for remove_useless_groupby_columns(), but we'd need it if we
> wanted to detect functional dependencies in
> check_functional_grouping() using unique indexes.
>

Thanks for the explanation. I will add the removal in the next version of
this
patch.

Best Regards
Andy Fan