Invent "join domains" to replace the below_outer_join hack.

EquivalenceClasses are now understood as applying within a "join
domain", which is a set of inner-joined relations (possibly underneath
an outer join).  We no longer need to treat an EC from below an outer
join as a second-class citizen.

I have hopes of eventually being able to treat outer-join clauses via
EquivalenceClasses, by means of only applying deductions within the
EC's join domain.  There are still problems in the way of that, though,
so for now the reconsider_outer_join_clause logic is still here.

I haven't been able to get rid of RestrictInfo.is_pushed_down either,
but I wonder if that could be recast using JoinDomains.

I had to hack one test case in postgres_fdw.sql to make it still test
what it was meant to, because postgres_fdw is inconsistent about
how it deals with quals containing non-shippable expressions; see
https://postgr.es/m/1691374.1671659838@sss.pgh.pa.us.  That should
be improved, but I don't think it's within the scope of this patch
series.

Patch by me; thanks to Richard Guo for review.

Discussion: https://postgr.es/m/830269.1656693747@sss.pgh.pa.us

Author: tglsfdc

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -2513,7 +2513,7 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.*, COALESCE(ft1.c3 || ft2.c3, 'foo
 ALTER SERVER loopback OPTIONS (DROP extensions);
 ALTER SERVER loopback OPTIONS (ADD fdw_startup_cost '10000.0');
 EXPLAIN (VERBOSE, COSTS OFF)
-SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND ft1.c1 = postgres_fdw_abs(ft2.c2))) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
+SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND (ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
                                                                                                                                                                                                                             QUERY PLAN                                                                                                                                                                                                                             
 -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  LockRows
@@ -2527,26 +2527,26 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.
                Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*
                ->  Foreign Scan
                      Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*
-                     Filter: (ft1.c1 = postgres_fdw_abs(ft2.c2))
+                     Filter: ((ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)
                      Relations: (public.ft1) INNER JOIN (public.ft2)
                      Remote SQL: SELECT r4."C 1", r4.c2, r4.c3, r4.c4, r4.c5, r4.c6, r4.c7, r4.c8, CASE WHEN (r4.*)::text IS NOT NULL THEN ROW(r4."C 1", r4.c2, r4.c3, r4.c4, r4.c5, r4.c6, r4.c7, r4.c8) END, CASE WHEN (r5.*)::text IS NOT NULL THEN ROW(r5."C 1", r5.c2, r5.c3, r5.c4, r5.c5, r5.c6, r5.c7, r5.c8) END, r5.c2 FROM ("S 1"."T 1" r4 INNER JOIN "S 1"."T 1" r5 ON (((r5."C 1" = r4."C 1")) AND ((r4."C 1" < 100)))) ORDER BY r4.c3 ASC NULLS LAST
                      ->  Sort
                            Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*, ft2.c2
                            Sort Key: ft1.c3
                            ->  Merge Join
                                  Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*, ft2.c2
-                                 Merge Cond: ((ft1.c1 = (postgres_fdw_abs(ft2.c2))) AND (ft1.c1 = ft2.c1))
+                                 Merge Cond: (ft1.c1 = ft2.c1)
+                                 Join Filter: ((ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)
                                  ->  Sort
                                        Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*
                                        Sort Key: ft1.c1
                                        ->  Foreign Scan on public.ft1
                                              Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*
                                              Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 100))
-                                 ->  Sort
-                                       Output: ft2.*, ft2.c1, ft2.c2, (postgres_fdw_abs(ft2.c2))
-                                       Sort Key: (postgres_fdw_abs(ft2.c2)), ft2.c1
+                                 ->  Materialize
+                                       Output: ft2.*, ft2.c1, ft2.c2
                                        ->  Foreign Scan on public.ft2
-                                             Output: ft2.*, ft2.c1, ft2.c2, postgres_fdw_abs(ft2.c2)
+                                             Output: ft2.*, ft2.c1, ft2.c2
                                              Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
 (32 rows)
 

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -681,7 +681,7 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.*, COALESCE(ft1.c3 || ft2.c3, 'foo
 ALTER SERVER loopback OPTIONS (DROP extensions);
 ALTER SERVER loopback OPTIONS (ADD fdw_startup_cost '10000.0');
 EXPLAIN (VERBOSE, COSTS OFF)
-SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND ft1.c1 = postgres_fdw_abs(ft2.c2))) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
+SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND (ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
 ALTER SERVER loopback OPTIONS (DROP fdw_startup_cost);
 ALTER SERVER loopback OPTIONS (ADD extensions 'postgres_fdw');
 

src/backend/nodes/outfuncs.c

@@ -468,7 +468,6 @@ _outEquivalenceClass(StringInfo str, const EquivalenceClass *node)
 	WRITE_BITMAPSET_FIELD(ec_relids);
 	WRITE_BOOL_FIELD(ec_has_const);
 	WRITE_BOOL_FIELD(ec_has_volatile);
-	WRITE_BOOL_FIELD(ec_below_outer_join);
 	WRITE_BOOL_FIELD(ec_broken);
 	WRITE_UINT_FIELD(ec_sortref);
 	WRITE_UINT_FIELD(ec_min_security);