Re: Support "Right Semi Join" plan shapes

Hi, Richard

> On Apr 25, 2024, at 11:28, Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
>
> Here is another rebase with a commit message to help review. I also
> tweaked some comments.

Thank you for updating the patch, here are some comments on the v5 patch.

+ /*
+ * For now we do not support RIGHT_SEMI join in mergejoin or nestloop
+ * join.
+ */
+ if (jointype == JOIN_RIGHT_SEMI)
+ return;
+

How about adding some reasons here?

+ * this is a right-semi join, or this is a right/right-anti/full join and
+ * there are nonmergejoinable join clauses. The executor's mergejoin

Maybe we can put the right-semi join together with the right/right-anti/full
join. Is there any other significance by putting it separately?

Maybe the following comments also should be updated. Right?

diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 5482ab85a7..791cbc551e 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -455,8 +455,8 @@ pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode,
* point of the available_rels machinations is to ensure that we only
* pull up quals for which that's okay.
*
- * We don't expect to see any pre-existing JOIN_SEMI, JOIN_ANTI, or
- * JOIN_RIGHT_ANTI jointypes here.
+ * We don't expect to see any pre-existing JOIN_SEMI, JOIN_ANTI,
+ * JOIN_RIGHT_SEMI, or JOIN_RIGHT_ANTI jointypes here.
*/
switch (j->jointype)
{
@@ -2951,6 +2951,7 @@ reduce_outer_joins_pass2(Node *jtnode,
* so there's no way that upper quals could refer to their
* righthand sides, and no point in checking. We don't expect
* to see JOIN_RIGHT_ANTI yet.
+ * Does JOIN_RIGHT_SEMI is expected here?
*/
break;
default: