Re: [PATCH] Keeps tracking the uniqueness with UniqueKey

On Fri, 3 Apr 2020 at 21:56, Andy Fan <zhihui.fan1213@gmail.com> wrote:
>
>
>
> On Fri, Apr 3, 2020 at 12:08 PM David Rowley <dgrowleyml@gmail.com> wrote:
>>
>> On Fri, 3 Apr 2020 at 16:40, Tom Lane <tgl@sss.pgh.pa.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.

There's no need for this patch to touch
remove_useless_groupby_columns().  Fixes for that should be considered
independently and *possibly* even backpatched.