Disable support for partitionwise joins in problematic cases.

Commit f49842d, which added support for partitionwise joins, built the
child's tlist by applying adjust_appendrel_attrs() to the parent's.  So in
the case where the parent's included a whole-row Var for the parent, the
child's contained a ConvertRowtypeExpr.  To cope with that, that commit
added code to the planner, such as setrefs.c, but some code paths still
assumed that the tlist for a scan (or join) rel would only include Vars
and PlaceHolderVars, which was true before that commit, causing errors:

* When creating an explicit sort node for an input path for a mergejoin
  path for a child join, prepare_sort_from_pathkeys() threw the 'could not
  find pathkey item to sort' error.
* When deparsing a relation participating in a pushed down child join as a
  subquery in contrib/postgres_fdw, get_relation_column_alias_ids() threw
  the 'unexpected expression in subquery output' error.
* When performing set_plan_references() on a local join plan generated by
  contrib/postgres_fdw for EvalPlanQual support for a pushed down child
  join, fix_join_expr() threw the 'variable not found in subplan target
  lists' error.

To fix these, two approaches have been proposed: one by Ashutosh Bapat and
one by me.  While the former keeps building the child's tlist with a
ConvertRowtypeExpr, the latter builds it with a whole-row Var for the
child not to violate the planner assumption, and tries to fix it up later,
But both approaches need more work, so refuse to generate partitionwise
join paths when whole-row Vars are involved, instead.  We don't need to
handle ConvertRowtypeExprs in the child's tlists for now, so this commit
also removes the changes to the planner.

Previously, partitionwise join computed attr_needed data for each child
separately, and built the child join's tlist using that data, which also
required an extra step for adding PlaceHolderVars to that tlist, but it
would be more efficient to build it from the parent join's tlist through
the adjust_appendrel_attrs() transformation.  So this commit builds that
list that way, and simplifies build_joinrel_tlist() and placeholder.c as
well as part of set_append_rel_size() to basically what they were before
partitionwise join went in.

Back-patch to PG11 where partitionwise join was introduced.

Report by Rajkumar Raghuwanshi.  Analysis by Ashutosh Bapat, who also
provided some of regression tests.  Patch by me, reviewed by Robert Haas.

Discussion: https://postgr.es/m/CAKcux6ktu-8tefLWtQuuZBYFaZA83vUzuRd7c1YHC-yEWyYFpg@mail.gmail.com

src/test/regress/expected/partition_aggregate.out

@@ -449,6 +449,38 @@ SELECT t1.x, sum(t1.y), count(*) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2
  24 |  900 |   100
 (5 rows)
 
+-- Check with whole-row reference; partitionwise aggregation does not apply
+EXPLAIN (COSTS OFF)
+SELECT t1.x, sum(t1.y), count(t1) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Sort
+   Sort Key: t1.x, (sum(t1.y)), (count(((t1.*)::pagg_tab1)))
+   ->  HashAggregate
+         Group Key: t1.x
+         ->  Hash Join
+               Hash Cond: (t1.x = t2.y)
+               ->  Append
+                     ->  Seq Scan on pagg_tab1_p1 t1
+                     ->  Seq Scan on pagg_tab1_p2 t1_1
+                     ->  Seq Scan on pagg_tab1_p3 t1_2
+               ->  Hash
+                     ->  Append
+                           ->  Seq Scan on pagg_tab2_p1 t2
+                           ->  Seq Scan on pagg_tab2_p2 t2_1
+                           ->  Seq Scan on pagg_tab2_p3 t2_2
+(15 rows)
+
+SELECT t1.x, sum(t1.y), count(t1) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
+ x  | sum  | count 
+----+------+-------
+  0 |  500 |   100
+  6 | 1100 |   100
+ 12 |  700 |   100
+ 18 | 1300 |   100
+ 24 |  900 |   100
+(5 rows)
+
 -- GROUP BY having other matching key
 EXPLAIN (COSTS OFF)
 SELECT t2.y, sum(t1.y), count(*) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t2.y ORDER BY 1, 2, 3;

src/test/regress/expected/partition_join.out

@@ -62,33 +62,28 @@ SELECT t1.a, t1.c, t2.b, t2.c FROM prt1 t1, prt2 t2 WHERE t1.a = t2.b AND t1.b =
  450 | 0450 | 450 | 0450
 (4 rows)
 
--- left outer join, with whole-row reference
+-- left outer join, with whole-row reference; partitionwise join does not apply
 EXPLAIN (COSTS OFF)
 SELECT t1, t2 FROM prt1 t1 LEFT JOIN prt2 t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
                     QUERY PLAN                    
 --------------------------------------------------
  Sort
    Sort Key: t1.a, t2.b
-   ->  Append
-         ->  Hash Right Join
-               Hash Cond: (t2.b = t1.a)
+   ->  Hash Right Join
+         Hash Cond: (t2.b = t1.a)
+         ->  Append
                ->  Seq Scan on prt2_p1 t2
-               ->  Hash
+               ->  Seq Scan on prt2_p2 t2_1
+               ->  Seq Scan on prt2_p3 t2_2
+         ->  Hash
+               ->  Append
                      ->  Seq Scan on prt1_p1 t1
                            Filter: (b = 0)
-         ->  Hash Right Join
-               Hash Cond: (t2_1.b = t1_1.a)
-               ->  Seq Scan on prt2_p2 t2_1
-               ->  Hash
                      ->  Seq Scan on prt1_p2 t1_1
                            Filter: (b = 0)
-         ->  Hash Right Join
-               Hash Cond: (t2_2.b = t1_2.a)
-               ->  Seq Scan on prt2_p3 t2_2
-               ->  Hash
                      ->  Seq Scan on prt1_p3 t1_2
                            Filter: (b = 0)
-(21 rows)
+(16 rows)
 
 SELECT t1, t2 FROM prt1 t1 LEFT JOIN prt2 t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
       t1      |      t2      
@@ -1042,6 +1037,40 @@ SELECT t1.a, t2.b FROM (SELECT * FROM prt1 WHERE a < 450) t1 LEFT JOIN (SELECT *
  400 |    
 (9 rows)
 
+-- merge join when expression with whole-row reference needs to be sorted;
+-- partitionwise join does not apply
+EXPLAIN (COSTS OFF)
+SELECT t1.a, t2.b FROM prt1 t1, prt2 t2 WHERE t1::text = t2::text AND t1.a = t2.b ORDER BY t1.a;
+                                       QUERY PLAN                                        
+-----------------------------------------------------------------------------------------
+ Merge Join
+   Merge Cond: ((t1.a = t2.b) AND (((((t1.*)::prt1))::text) = ((((t2.*)::prt2))::text)))
+   ->  Sort
+         Sort Key: t1.a, ((((t1.*)::prt1))::text)
+         ->  Result
+               ->  Append
+                     ->  Seq Scan on prt1_p1 t1
+                     ->  Seq Scan on prt1_p2 t1_1
+                     ->  Seq Scan on prt1_p3 t1_2
+   ->  Sort
+         Sort Key: t2.b, ((((t2.*)::prt2))::text)
+         ->  Result
+               ->  Append
+                     ->  Seq Scan on prt2_p1 t2
+                     ->  Seq Scan on prt2_p2 t2_1
+                     ->  Seq Scan on prt2_p3 t2_2
+(16 rows)
+
+SELECT t1.a, t2.b FROM prt1 t1, prt2 t2 WHERE t1::text = t2::text AND t1.a = t2.b ORDER BY t1.a;
+ a  | b  
+----+----
+  0 |  0
+  6 |  6
+ 12 | 12
+ 18 | 18
+ 24 | 24
+(5 rows)
+
 RESET enable_hashjoin;
 RESET enable_nestloop;
 --

src/test/regress/sql/partition_aggregate.sql

@@ -111,6 +111,11 @@ EXPLAIN (COSTS OFF)
 SELECT t1.x, sum(t1.y), count(*) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
 SELECT t1.x, sum(t1.y), count(*) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
 
+-- Check with whole-row reference; partitionwise aggregation does not apply
+EXPLAIN (COSTS OFF)
+SELECT t1.x, sum(t1.y), count(t1) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
+SELECT t1.x, sum(t1.y), count(t1) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t1.x ORDER BY 1, 2, 3;
+
 -- GROUP BY having other matching key
 EXPLAIN (COSTS OFF)
 SELECT t2.y, sum(t1.y), count(*) FROM pagg_tab1 t1, pagg_tab2 t2 WHERE t1.x = t2.y GROUP BY t2.y ORDER BY 1, 2, 3;

src/test/regress/sql/partition_join.sql

@@ -34,7 +34,7 @@ EXPLAIN (COSTS OFF)
 SELECT t1.a, t1.c, t2.b, t2.c FROM prt1 t1, prt2 t2 WHERE t1.a = t2.b AND t1.b = 0 ORDER BY t1.a, t2.b;
 SELECT t1.a, t1.c, t2.b, t2.c FROM prt1 t1, prt2 t2 WHERE t1.a = t2.b AND t1.b = 0 ORDER BY t1.a, t2.b;
 
--- left outer join, with whole-row reference
+-- left outer join, with whole-row reference; partitionwise join does not apply
 EXPLAIN (COSTS OFF)
 SELECT t1, t2 FROM prt1 t1 LEFT JOIN prt2 t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
 SELECT t1, t2 FROM prt1 t1 LEFT JOIN prt2 t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
@@ -160,6 +160,12 @@ EXPLAIN (COSTS OFF)
 SELECT t1.a, t2.b FROM (SELECT * FROM prt1 WHERE a < 450) t1 LEFT JOIN (SELECT * FROM prt2 WHERE b > 250) t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
 SELECT t1.a, t2.b FROM (SELECT * FROM prt1 WHERE a < 450) t1 LEFT JOIN (SELECT * FROM prt2 WHERE b > 250) t2 ON t1.a = t2.b WHERE t1.b = 0 ORDER BY t1.a, t2.b;
 
+-- merge join when expression with whole-row reference needs to be sorted;
+-- partitionwise join does not apply
+EXPLAIN (COSTS OFF)
+SELECT t1.a, t2.b FROM prt1 t1, prt2 t2 WHERE t1::text = t2::text AND t1.a = t2.b ORDER BY t1.a;
+SELECT t1.a, t2.b FROM prt1 t1, prt2 t2 WHERE t1::text = t2::text AND t1.a = t2.b ORDER BY t1.a;
+
 RESET enable_hashjoin;
 RESET enable_nestloop;