Fix incorrect handling of join clauses pushed into parameterized paths.

In some cases a clause attached to an outer join can be pushed down into
the outer join's RHS even though the clause is not degenerate --- this
can happen if we choose to make a parameterized path for the RHS.  If
the clause ends up attached to a lower outer join, we'd misclassify it
as being a "join filter" not a plain "filter" condition at that node,
leading to wrong query results.

To fix, teach extract_actual_join_clauses to examine each join clause's
required_relids, not just its is_pushed_down flag.  (The latter now
seems vestigial, or at least in need of rethinking, but we won't do
anything so invasive as redefining it in a bug-fix patch.)

This has been wrong since we introduced parameterized paths in 9.2,
though it's evidently hard to hit given the lack of previous reports.
The test case used here involves a lateral function call, and I think
that a lateral reference may be required to get the planner to select
a broken plan; though I wouldn't swear to that.  In any case, even if
LATERAL is needed to trigger the bug, it still affects all supported
branches, so back-patch to all.

Per report from Andreas Karlsson.  Thanks to Andrew Gierth for
preliminary investigation.

Discussion: https://postgr.es/m/f8128b11-c5bf-3539-48cd-234178b2314d@proxel.se

2 files changed, 38 insertions, 0 deletions

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 84c6e9b5a40..cbc882d47ba 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3371,6 +3371,33 @@ order by fault;
          | 123 |   122
 (1 row)
 
+explain (costs off)
+select * from
+(values (1, array[10,20]), (2, array[20,30])) as v1(v1x,v1ys)
+left join (values (1, 10), (2, 20)) as v2(v2x,v2y) on v2x = v1x
+left join unnest(v1ys) as u1(u1y) on u1y = v2y;
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Nested Loop Left Join
+   ->  Values Scan on "*VALUES*"
+   ->  Hash Right Join
+         Hash Cond: (u1.u1y = "*VALUES*_1".column2)
+         Filter: ("*VALUES*_1".column1 = "*VALUES*".column1)
+         ->  Function Scan on unnest u1
+         ->  Hash
+               ->  Values Scan on "*VALUES*_1"
+(8 rows)
+
+select * from
+(values (1, array[10,20]), (2, array[20,30])) as v1(v1x,v1ys)
+left join (values (1, 10), (2, 20)) as v2(v2x,v2y) on v2x = v1x
+left join unnest(v1ys) as u1(u1y) on u1y = v2y;
+ v1x |  v1ys   | v2x | v2y | u1y 
+-----+---------+-----+-----+-----
+   1 | {10,20} |   1 |  10 |  10
+   2 | {20,30} |   2 |  20 |  20
+(2 rows)
+
 --
 -- test handling of potential equivalence clauses above outer joins
 --
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index b1e05a33bd3..86c6d5be283 100644
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1028,6 +1028,17 @@ select * from
 where fault = 122
 order by fault;
 
+explain (costs off)
+select * from
+(values (1, array[10,20]), (2, array[20,30])) as v1(v1x,v1ys)
+left join (values (1, 10), (2, 20)) as v2(v2x,v2y) on v2x = v1x
+left join unnest(v1ys) as u1(u1y) on u1y = v2y;
+
+select * from
+(values (1, array[10,20]), (2, array[20,30])) as v1(v1x,v1ys)
+left join (values (1, 10), (2, 20)) as v2(v2x,v2y) on v2x = v1x
+left join unnest(v1ys) as u1(u1y) on u1y = v2y;
+
 --
 -- test handling of potential equivalence clauses above outer joins
 --