Re: Support "Right Semi Join" plan shapes - Mailing list pgsql-hackers

On Fri, Jun 28, 2024 at 2:54 PM Richard Guo <guofenglinux@gmail.com> wrote:
> On Mon, Jun 24, 2024 at 5:59 PM Richard Guo <guofenglinux@gmail.com> wrote:
> > I noticed that this patch changes the plan of a query in join.sql from
> > a semi join to right semi join, compromising the original purpose of
> > this query, which was to test the fix for neqjoinsel's behavior for
> > semijoins (see commit 7ca25b7d).
> >
> > --
> > -- semijoin selectivity for <>
> > --
> > explain (costs off)
> > select * from int4_tbl i4, tenk1 a
> > where exists(select * from tenk1 b
> >              where a.twothousand = b.twothousand and a.fivethous <> b.fivethous)
> >       and i4.f1 = a.tenthous;
> >
> > So I've changed this test case a bit so that it is still testing what it
> > is supposed to test.
>
> I've refined this test case further to make it more stable by using an
> additional filter 'a.tenthous < 5000'.  Besides, I noticed a surplus
> blank line in ExecHashJoinImpl().  I've removed it in the v7 patch.

BTW, I've also verified the empty-rel optimization for hash join and
AFAICT it works correctly for the new right-semi join.

Thanks
Richard