Horton

Re: Support "Right Semi Join" plan shapes

Japin Li <japinli@hotmail.com>

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From: Li Japin <japinli@hotmail.com>
To: Richard Guo <guofenglinux@gmail.com>
Cc: Alena Rybakina <lena.ribackina@yandex.ru>, wenhui qiu <qiuwenhuifx@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, vignesh C <vignesh21@gmail.com>
Date: 2024-06-24T05:27:54Z
Lists: pgsql-hackers

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  1. Support "Right Semi Join" plan shapes

  2. Fix neqjoinsel's behavior for semi/anti join cases.

Hi, Richard

> On Apr 25, 2024, at 11:28, Richard Guo <guofenglinux@gmail.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: