Fix generation of EC join conditions at the wrong plan level.

get_baserel_parampathinfo previously assumed without checking that
the results of generate_join_implied_equalities "necessarily satisfy
join_clause_is_movable_into".  This turns out to be wrong in the
presence of outer joins, because the generated clauses could include
Vars that mustn't be evaluated below a relevant outer join.  That
led to applying clauses at the wrong plan level and possibly getting
incorrect query results.  We must check each clause's nullable_relids,
and really the right thing to do is test join_clause_is_movable_into.

However, trying to fix it that way exposes an oversight in
equivclass.c: it wasn't careful about marking join clauses for
appendrel children with the correct clause_relids.  That caused the
modified get_baserel_parampathinfo code to reject some clauses it
still needs to accept.  (See parallel commit for HEAD/v16 for more
commentary about that.)

Per bug #18429 from Benoît Ryder.  This misbehavior existed for
a long time before commit 2489d76c4, so patch v12-v15 this way.

Discussion: https://postgr.es/m/18429-8982d4a348cc86c6@postgresql.org

2 files changed, 50 insertions, 0 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 8eaa964d462..2eca3782e60 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -5949,6 +5949,37 @@ select * from
  3 | 3
 (6 rows)
 
+-- check for generation of join EC conditions at wrong level (bug #18429)
+explain (costs off)
+select * from (
+  select arrayd.ad, coalesce(c.hundred, 0) as h
+  from unnest(array[1]) as arrayd(ad)
+  left join lateral (
+    select hundred from tenk1 where unique2 = arrayd.ad
+  ) c on true
+) c2
+where c2.h * c2.ad = c2.h * (c2.ad + 1);
+                                              QUERY PLAN                                               
+-------------------------------------------------------------------------------------------------------
+ Nested Loop Left Join
+   Filter: ((COALESCE(tenk1.hundred, 0) * arrayd.ad) = (COALESCE(tenk1.hundred, 0) * (arrayd.ad + 1)))
+   ->  Function Scan on unnest arrayd
+   ->  Index Scan using tenk1_unique2 on tenk1
+         Index Cond: (unique2 = arrayd.ad)
+(5 rows)
+
+select * from (
+  select arrayd.ad, coalesce(c.hundred, 0) as h
+  from unnest(array[1]) as arrayd(ad)
+  left join lateral (
+    select hundred from tenk1 where unique2 = arrayd.ad
+  ) c on true
+) c2
+where c2.h * c2.ad = c2.h * (c2.ad + 1);
+ ad | h 
+----+---
+(0 rows)
+
 -- check the number of columns specified
 SELECT * FROM (int8_tbl i cross join int4_tbl j) ss(a,b,c,d);
 ERROR:  join expression "ss" has 3 columns available but 4 columns specified
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index f8ed53fcc43..9d622d18a12 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -2029,6 +2029,25 @@ select * from
    (select q1.v)
   ) as q2;
 
+-- check for generation of join EC conditions at wrong level (bug #18429)
+explain (costs off)
+select * from (
+  select arrayd.ad, coalesce(c.hundred, 0) as h
+  from unnest(array[1]) as arrayd(ad)
+  left join lateral (
+    select hundred from tenk1 where unique2 = arrayd.ad
+  ) c on true
+) c2
+where c2.h * c2.ad = c2.h * (c2.ad + 1);
+select * from (
+  select arrayd.ad, coalesce(c.hundred, 0) as h
+  from unnest(array[1]) as arrayd(ad)
+  left join lateral (
+    select hundred from tenk1 where unique2 = arrayd.ad
+  ) c on true
+) c2
+where c2.h * c2.ad = c2.h * (c2.ad + 1);
+
 -- check the number of columns specified
 SELECT * FROM (int8_tbl i cross join int4_tbl j) ss(a,b,c,d);