Re: BUG #17700: An assert failed in prepjointree.c

On Tue, Nov 29, 2022 at 8:12 AM Richard Guo <guofenglinux@gmail.com> wrote:

> On Tue, Nov 29, 2022 at 12:22 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
>> Actually ... it seems like we could just drop that Assert, as per
>> revised argument in the comment.  This'd explain the lack of field
>> complaints: there's no bug in a production build.
>
>
> Ah yes, that's right.  We can be sure that above the semijoin there
> would be no reference to its RHS.  And the PHV in semijoin's qual seems
> unnecessary.
>
> This reminds me of another question I had about unwrapping unnecessary
> PHVs [1].  Sad that we don't have infrastructure for that.
>

BTW, for the test case

+explain (verbose, costs off)
+with ctetable as not materialized ( select 1 as f1 )
+select * from ctetable c1
+where f1 in ( select c3.f1 from ctetable c2 full join ctetable c3 on true
);

Actually we just need to keep 'c3' in a join's nullable side to have the
PHV created.  So we don't have to use full join in the subquery.  A left
join would do.

Thanks
Richard