From d6c782dde374cc0ff1b1feae7d751066a1db8417 Mon Sep 17 00:00:00 2001
From: Richard Guo <guofenglinux@gmail.com>
Date: Tue, 7 Nov 2023 10:50:00 +0800
Subject: [PATCH v1] Fix mismatched nullingrels when inlining functions

When we optimize field selection from a whole-row Var into a simple Var
while simplifying functions, we failed to propagate the nullingrels into
the new Var.  This patch fixes that.

Per report from Marian Krucina in BUG #18184
---
 src/backend/optimizer/util/clauses.c | 20 ++++++++++++++------
 src/test/regress/expected/join.out   | 20 ++++++++++++++++++++
 src/test/regress/sql/join.sql        | 10 ++++++++++
 3 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index da258968b8..6b3e712905 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -3296,12 +3296,20 @@ eval_const_expressions_mutator(Node *node,
 											  fselect->resulttype,
 											  fselect->resulttypmod,
 											  fselect->resultcollid))
-						return (Node *) makeVar(((Var *) arg)->varno,
-												fselect->fieldnum,
-												fselect->resulttype,
-												fselect->resulttypmod,
-												fselect->resultcollid,
-												((Var *) arg)->varlevelsup);
+					{
+						Var	   *newvar;
+
+						newvar = makeVar(((Var *) arg)->varno,
+										 fselect->fieldnum,
+										 fselect->resulttype,
+										 fselect->resulttypmod,
+										 fselect->resultcollid,
+										 ((Var *) arg)->varlevelsup);
+
+						newvar->varnullingrels = ((Var *) arg)->varnullingrels;
+
+						return (Node *) newvar;
+					}
 				}
 				if (arg && IsA(arg, RowExpr))
 				{
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 892ea5f170..52fe18d5fa 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -2687,6 +2687,26 @@ select * from onek t1
                            Filter: (two = t2.two)
 (11 rows)
 
+--
+-- check for correct handling of nullingrels when simplifying functions
+--
+create function f_immutable_nullingrels(t onek) returns text as
+$$ select t.unique1::text; $$ language sql immutable;
+explain (costs off)
+select f_immutable_nullingrels(t2) from onek t1
+    left join onek t2 on t1.unique1 = t2.unique1
+    left join onek t3 on true;
+                        QUERY PLAN                         
+-----------------------------------------------------------
+ Nested Loop Left Join
+   ->  Merge Left Join
+         Merge Cond: (t1.unique1 = t2.unique1)
+         ->  Index Only Scan using onek_unique1 on onek t1
+         ->  Index Only Scan using onek_unique1 on onek t2
+   ->  Materialize
+         ->  Index Only Scan using onek_hundred on onek t3
+(7 rows)
+
 --
 -- check a case where we formerly got confused by conflicting sort orders
 -- in redundant merge join path keys
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 559c36dc07..80169f9efb 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -550,6 +550,16 @@ select * from onek t1
       (select * from onek t3 where t3.two = t2.two offset 0) s
       on t2.unique1 = 1;
 
+--
+-- check for correct handling of nullingrels when simplifying functions
+--
+create function f_immutable_nullingrels(t onek) returns text as
+$$ select t.unique1::text; $$ language sql immutable;
+explain (costs off)
+select f_immutable_nullingrels(t2) from onek t1
+    left join onek t2 on t1.unique1 = t2.unique1
+    left join onek t3 on true;
+
 --
 -- check a case where we formerly got confused by conflicting sort orders
 -- in redundant merge join path keys
-- 
2.31.0